constraints: Don't apply titlebar constraint on non-drag user-op move

2d8fa26c8e ("core: Pass "frame action" grab operations as an
"unconstrained" grab op") changed the behaviour to treat non-grab
related window moving that has the "user action" flag set to still apply
the "constrain_titlebar_visible" constraint.

The fact that it wasn't applied before was relied upon by some
extensions. While it should arguably exist a better API that for such
extensions to use that have a bit more predictable behavior, until that
is so, restore the old semantics.

Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/2891>

src/core/constraints.c

@@ -1778,9 +1778,9 @@ constrain_titlebar_visible (MetaWindow         *window,
    */
   unconstrained_user_action =
     info->is_user_action &&
-    window_drag &&
-    (meta_window_drag_get_grab_op (window_drag) &
-     META_GRAB_OP_WINDOW_FLAG_UNCONSTRAINED) != 0;
+    (!window_drag ||
+     (meta_window_drag_get_grab_op (window_drag) &
+      META_GRAB_OP_WINDOW_FLAG_UNCONSTRAINED) != 0);
 
   /* Exit early if we know the constraint won't apply--note that this constraint
    * is only meant for normal windows (e.g. we don't want docks to be shoved