Remove extra execution of blkid for any unreported paths (#131)

Again on Fedora 31 with a slightly different disk layout to the previous
commit.  sdb is partitioned with 1 empty partition and sdc remains
completely empty:
    # lsblk -o name,maj:min,rm,size,ro,type,fstype,label,mountpoint
    NAME            MAJ:MIN RM  SIZE RO TYPE FSTYPE      LABEL MOUNTPOINT
    sda               8:0    0   20G  0 disk
    |-sda1            8:1    0    1G  0 part ext4              /boot
    \-sda2            8:2    0   19G  0 part LVM2_member
      |-fedora-root 253:0    0   17G  0 lvm  ext4              /
      \-fedora-swap 253:1    0    2G  0 lvm  swap              [SWAP]
    sdb               8:16   0    8G  0 disk
    \-sdb1            8:17   0    1G  0 part
    sdc               8:32   0    8G  0 disk
    sr0              11:0    1 1024M  0 rom
    # blkid -v
    blkid from util-linux 2.34  (libblkid 2.34.0, 14-Jun-2019)
    # blkid /dev/sda /dev/sda1 /dev/sda2 /dev/sdb /dev/sdb1 /dev/sdc
    /dev/sda: PTUUID="5012fb1f" PTTYPE="dos"
    /dev/sda1: UUID="3cd48816-7817-4636-9fec-5f1afe76c1b2" TYPE="ext4" PARTUUID="5012fb1f-01"
    /dev/sda2: UUID="PH94ej-C8xU-bnMJ-UIh8-ZimI-4B7f-dHlZxh" TYPE="LVM2_member" PARTUUID="5012fb1f-02"
    /dev/sdb: PTUUID="1d120b57" PTTYPE="dos"
    /dev/sdb1: PARTUUID="1d120b57-01"

Stracing GParted shows these executions of blkid:
    # strace -f -q -bexecve -eexecve ./gpartedbin 2>&1 1> /dev/null | egrep -v 'ENOENT|SIGCHLD'
    ...
    [pid 160040] execve("/usr/sbin/blkid", ["blkid", "/dev/sda", "/dev/sda1", "/dev/sda2", "/dev/sdb", "/dev/sdb1", "/dev/sdc"], 0xa4e1b0 /* 32 vars */ <detached ...>
    [pid 160041] execve("/usr/sbin/blkid", ["blkid", "/dev/sdc"], 0xa4e1b0 /* 32 vars */ <detached ...>
    ...

On Fedora 31 with blkid from util-linux 2.34 it reports information for
sdb (partitioned drive) and sdb1 (empty partition) with only no
information for sdc (empty whole disk drive).  Hence no FS_Info cache
entry and re-execution of blkid just for sdc.

On older CentOS 7 with the same disk layout blkid reports this:
    # blkid -v
    blkid from util-linux 2.23.2  (libblkid 2.23.0, 25-Apr-2013)
    # blkid /dev/sda /dev/sda1 /dev/sda2 /dev/sdb /dev/sdb1 /dev/sdc
    /dev/sda: PTTYPE="dos"
    /dev/sda1: UUID="e7d559e4-3e1d-4fbc-b034-3fdeb498f44d" TYPE="xfs"
    /dev/sda2: UUID="B7ODFx-BfTE-hq7N-UlrF-f5ML-CPRe-klSy26" TYPE="LVM2_member"
    /dev/sdb: PTTYPE="dos"

And stracing GParted shows these executions of blkid:
    # strace -f -q -bexecve -eexecve ./gpartedbin 2>&1 1> /dev/null | egrep -v 'ENOENT|SIGCHLD'
    ...
    [pid  1889] execve("/sbin/blkid", ["blkid", "/dev/sda", "/dev/sda1", "/dev/sda2", "/dev/sdb", "/dev/sdb1", "/dev/sdc"], 0x10b8b10 /* 26 vars */ <detached ...>
    [pid  1890] execve("/sbin/blkid", ["blkid", "/dev/sdb1"], 0x10b8b10 /* 26 vars */ <detached ...>
    [pid  1891] execve("/sbin/blkid", ["blkid", "/dev/sdc"], 0x10b8b10 /* 26 vars */ <detached ...>
...

This time on CentOS 7 with blkid from util-linux 2.23.2 it reports
information for only sdb (partitioned drive), but not sdb1 (empty
partition) or sdc (empty whole disk drive).  Hence no FS_info cache
entries and re-execution of blkid for both sdb1 and sdc.

GParted needs blkid identification of file system images, LVM Logical
Volumes or any other partitions named on the command line which it
wouldn't normally scan [1].  Now every name of interest is passed to
blkid, additional executions of blkid won't get any extra information
and are redundant.  Therefore remove this unnecessary code.

Note that these last 2 commits remove creation of "blank" cache entries
(just block special with blank fstype and other attributes) when blkid
reports no information for a particular path.  Those entry were needed
to suppress unnecessary additional execution of blkid.  However now that
blkid is only executed once (excluding querying the label) this is no
longer necessary.  All the getter functions return suitable blank values
when no cache entry is found.

[1] e8f0504b13
    Make sure that FS_Info cache is loaded for all named paths (#787181)

Closes #131 - GParted hangs when non-named device is hung

include/FS_Info.h

@@ -50,7 +50,6 @@ private:
 	static void set_commands_found();
 	static const FS_Entry & get_cache_entry_by_path( const Glib::ustring & path );
 	static void load_fs_info_cache(const std::vector<Glib::ustring>& paths);
-	static void load_fs_info_cache_extra_for_path( const Glib::ustring & path );
 	static bool run_blkid_load_cache(const std::vector<Glib::ustring>& paths);
 	static void update_fs_info_cache_all_labels();
 	static bool run_blkid_update_cache_one_label( FS_Entry & fs_entry );

src/FS_Info.cc

@@ -55,19 +55,9 @@ void FS_Info::load_cache_for_paths(const std::vector<Glib::ustring>& paths)
 	set_commands_found();
 	load_fs_info_cache(paths);
 	fs_info_cache_initialized = true;
-
-	const BlockSpecial empty_bs = BlockSpecial();
-	for (unsigned int i = 0; i < paths.size(); i++)
-	{
-		const FS_Entry& fs_entry = get_cache_entry_by_path(paths[i]);
-		if ( fs_entry.path == empty_bs )
-		{
-			// Run "blkid PATH" and load entry into cache for missing entries.
-			load_fs_info_cache_extra_for_path(paths[i]);
-		}
-	}
 }
 
+
 // Retrieve the file system type for the path
 Glib::ustring FS_Info::get_fs_type( const Glib::ustring & path )
 {
@@ -112,8 +102,7 @@ Glib::ustring FS_Info::get_label( const Glib::ustring & path, bool & found )
 			{
 				// Already have the label or this is a blank cache entry
 				// for a whole disk device containing a partition table,
-				// so no label (as created by
+				// so no label.
-				// load_fs_info_cache_extra_for_path()).
 				found = fs_info_cache[i].have_label;
 				return fs_info_cache[i].label;
 			}
@@ -213,21 +202,6 @@ void FS_Info::load_fs_info_cache(const std::vector<Glib::ustring>& paths)
 }
 
 
-void FS_Info::load_fs_info_cache_extra_for_path( const Glib::ustring & path )
-{
-	std::vector<Glib::ustring> one_path;
-	one_path.push_back(path);
-	bool entry_added = run_blkid_load_cache(one_path);
-	if ( ! entry_added )
-	{
-		// Ran "blkid PATH" but didn't find details suitable for loading as a
-		// cache entry so add a blank entry for PATH name here.
-		FS_Entry fs_entry = {BlockSpecial( path ), "", "", "", false, ""};
-		fs_info_cache.push_back( fs_entry );
-	}
-}
-
-
 bool FS_Info::run_blkid_load_cache(const std::vector<Glib::ustring>& paths)
 {
 	// Parse blkid output line by line extracting mandatory field: path and optional