Fix Quartz Full Screen Crash.

gdk/quartz/GdkQuartzNSWindow.c

@@ -23,6 +23,14 @@
 
 @implementation GdkQuartzNSWindow
 
+- (void)windowWillClose:(NSNotification*)notification
+{
+  // Clears the delegate when window is going to be closed; since EL
+  // Capitan it is possible that the methods of delegate would get
+  // called after the window has been closed.
+  [self setDelegate:nil];
+}
+
 -(BOOL)windowShouldClose:(id)sender
 {
   GdkWindow *window = [[self contentView] gdkWindow];

gdk/quartz/GdkQuartzView.c

@@ -662,7 +662,7 @@
   GdkWindowImplQuartz *impl = GDK_WINDOW_IMPL_QUARTZ (gdk_window->impl);
   NSRect rect;
 
-  if (!impl->toplevel)
+  if (!impl || !impl->toplevel)
     return;
 
   if (trackingRect)