Allow empty needle in BidiTrieContainer.lastIndexOf()

Related issue:
- https://github.com/uBlockOrigin/uBlock-issues/issues/882

Related commit:
- https://github.com/gorhill/uBlock/commit/7c0294bd5f54

The changes in the commit above have been reverted, and
the new fix is to add the ability to handle an empty
needle in BidiTrieContainer.lastIndexOf() -- in which
case the method will return the end of the currently
matched pattern.

src/js/static-net-filtering.js

@@ -2599,20 +2599,6 @@ const FilterParser = class {
         this.token = matches[0];
         this.tokenHash = urlTokenizer.tokenHashFromString(this.token);
         this.tokenBeg = matches.index;
-
-        // https://www.reddit.com/r/uBlockOrigin/comments/dpcvfx/
-        //   Since we found a valid token, we can get rid of trailing
-        //   wildcards if any.
-        if ( this.firstWildcardPos !== -1 ) {
-            const lastCharPos = this.f.length - 1;
-            if ( this.firstWildcardPos === lastCharPos ) {
-                this.f = this.f.slice(0, -1);
-                this.firstWildcardPos = -1;
-            } else if ( this.secondWildcardPos === lastCharPos ) {
-                this.f = this.f.slice(0, -1);
-                this.secondWildcardPos = -1;
-            }
-        }
     }
 
     findGoodToken() {

src/js/strie.js

@@ -666,6 +666,7 @@ const roundToPageSize = v => (v + PAGE_SIZE-1) & ~(PAGE_SIZE-1);
     // Find the right-most instance of substring in main string.
     // WASMable.
     lastIndexOf(haystackBeg, haystackEnd, needleLeft, needleLen) {
+        if ( needleLen === 0 ) { return haystackBeg; }
         let haystackLeft = haystackEnd - needleLen;
         if ( haystackLeft < haystackBeg ) { return -1; }
         needleLeft += this.buf32[CHAR0_SLOT];

src/js/wasm/biditrie.wat

@@ -639,6 +639,13 @@
     (local $i i32)
     (local $j i32)
     (local $c0 i32)
+    ;; if ( needleLen === 0 ) { return haystackBeg; }
+    get_local $needleLen
+    i32.eqz
+    if
+        get_local $haystackBeg
+        return
+    end
     block $fail
     block $succeed
     ;; let haystackLeft = haystackEnd - needleLen;