frames: Fix XGetWMNormalHints return value check

It returns non-0 if there are any hints in the WM_NORMAL_HINTS
property, 0 if there are none.

Fixes the mouse cursor changing to the resize shape over the decorations
of non-resizable windows.

Fixes: c7b3d8c607 ("frames: Push error traps around various X11 calls")
Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/3096>

src/frames/meta-frame.c

@@ -446,10 +446,10 @@ frame_sync_wm_normal_hints (GtkWindow *frame,
 
   gdk_x11_display_error_trap_push (display);
 
-  if (XGetWMNormalHints (gdk_x11_display_get_xdisplay (display),
-                         client_window,
-                         &size_hints,
-                         &nitems) != Success)
+  if (!XGetWMNormalHints (gdk_x11_display_get_xdisplay (display),
+                          client_window,
+                          &size_hints,
+                          &nitems))
     {
       gdk_x11_display_error_trap_pop_ignored (display);
       return;