quartz: Update GL context on window resize

The previous version of this patch sent an update message to the
NSOpenGLContext in a GdkGLContext::update vfunc, but that vfunc does not
exist any more.

See: #517

gdk/quartz/gdkwindow-quartz.c

@@ -26,6 +26,7 @@
 #include "gdkwindowimpl.h"
 #include "gdkprivate-quartz.h"
 #include "gdkglcontext-quartz.h"
+#include "gdkquartzglcontext.h"
 #include "gdkquartzscreen.h"
 #include "gdkquartzcursor.h"
 
@@ -1324,6 +1325,9 @@ move_resize_window_internal (GdkWindow *window,
         }
     }
 
+  if (window->gl_paint_context != NULL)
+    [GDK_QUARTZ_GL_CONTEXT (window->gl_paint_context)->gl_context update];
+
   GDK_QUARTZ_RELEASE_POOL;
 }