Check whether VFS provides an open_archive() method.

Signed-off-by: Ilia Maslakov <il.smind@gmail.com>

lib/vfs/direntry.c

@@ -1067,6 +1067,7 @@ vfs_s_get_path_mangle (struct vfs_class *me, char *inname, struct vfs_s_super **
         ERRNOR (EIO, NULL);
 
     super = vfs_s_new_super (me);
+    if (MEDATA->open_archive != NULL)
         result = MEDATA->open_archive (me, super, archive_name, op);
     if (result == -1)
     {