[mutter] window: Filter out buttons when checking if the event is unmodified

[Jasper St. Pierre <jstpierre src gnome org>]

commit a5f993f269f30dd555dfb04bec985a6643b43012
Author: Jasper St. Pierre <jstpierre mecheye net>
Date:   Fri Aug 15 08:39:01 2014 -0400

    window: Filter out buttons when checking if the event is unmodified

 src/core/window.c |    6 +++++-
 1 files changed, 5 insertions(+), 1 deletions(-)
---
diff --git a/src/core/window.c b/src/core/window.c
index 2fd48d2..92ea731 100644
--- a/src/core/window.c
+++ b/src/core/window.c
@@ -7912,7 +7912,11 @@ meta_window_handle_ungrabbed_event (MetaWindow         *window,
    * care about. Just let the event through.
    */
 
-  unmodified = event->button.modifier_state == 0;
+  const int CLUTTER_BUTTON_MASK = (CLUTTER_BUTTON1_MASK | CLUTTER_BUTTON2_MASK |
+                                   CLUTTER_BUTTON3_MASK | CLUTTER_BUTTON4_MASK |
+                                   CLUTTER_BUTTON5_MASK);
+
+  unmodified = (event->button.modifier_state & ~CLUTTER_BUTTON_MASK) == 0;
   is_window_grab = button_event_is_window_grab (display, event);
 
   if (unmodified)