BFS: Implement the trivial case of Volume::CheckForLiveQuery.

Saves a bit of work when there are no live queries running
(as will often be the case on an idle system.)

src/add-ons/kernel/file_systems/bfs/Volume.cpp

@@ -456,8 +456,9 @@ Volume::UpdateLiveQueriesRenameMove(Inode* inode, ino_t oldDirectoryID,
 bool
 Volume::CheckForLiveQuery(const char* attribute)
 {
+	MutexLocker _(fQueryLock);
 	// TODO: check for a live query that depends on the specified attribute
-	return true;
+	return !fQueries.IsEmpty();
 }