fix logic in tag check, AND -> OR

Signed-off-by: Riccardo Spagni <ric@spagni.net>

src/version.cmake

@@ -7,7 +7,7 @@ if(RET)
 else()
 	message(STATUS "You are currently on commit ${COMMIT}")
 	execute_process(COMMAND "${GIT}" show-ref --tags -d --abbrev COMMAND awk "END{print $1}" RESULT_VARIABLE RET OUTPUT_VARIABLE TAGGEDCOMMIT OUTPUT_STRIP_TRAILING_WHITESPACE)
-	if(RET AND NOT TAGGEDCOMMIT)
+	if(RET OR NOT TAGGEDCOMMIT)
 	    message(WARNING "Cannot determine most recent tag. Make sure that you are building either from a Git working tree or from a source archive.")
 	    set(VERSIONTAG "${COMMIT}")
 	else()