Fix #147009: Anim: Normalize All fails when all groups are unlocked

When all vertex groups are *unlocked* and the Normalize All operator is
run with "Lock Active" disabled, the operator would fail with the
patently false error message "All groups are locked".

The cause was that:

1. When all vertex groups are unlocked, the lock flags array used
   internally would be left empty, with the idea that a non-existent
   flag indicates "unlocked".
2. The code that determined if all groups were locked was checking
   if any of those flags were "unlocked".
3. In an empty array, of course no items are "unlocked", and thus
   it would think all items are locked.

The fix in this PR is to also check if the flag array is empty when
determining if all groups are locked.

Pull Request: https://projects.blender.org/blender/blender/pulls/147272

source/blender/editors/object/object_vgroup.cc

@@ -1430,7 +1430,7 @@ static bool vgroup_normalize_all(Object *ob,
     soft_lock_flags[def_nr] = true;
   }
 
-  const bool all_locked = !lock_flags.contains(false);
+  const bool all_locked = !lock_flags.is_empty() && !lock_flags.contains(false);
   if (all_locked) {
     BKE_report(reports, RPT_ERROR, "All groups are locked");
   }