minimal_macosx: make sure theWindow object exists before sending it an event.

(cherry picked from commit bf355d950d86b8ae819dff0b1915fe1f655e7d64)
Signed-off-by: Derk-Jan Hartman <hartman@videolan.org>

modules/gui/minimal_macosx/voutagl.m

@@ -233,6 +233,7 @@ int aglManage( vout_thread_t * p_vout )
             aglSetViewport(p_vout, viewBounds, clipBounds);
 
             /* Most Carbon APIs are not thread-safe, therefore delagate some GUI visibilty update to the main thread */
+            if( p_vout->p_sys->theWindow )
                 sendEventToMainThread(GetWindowEventTarget(p_vout->p_sys->theWindow), kEventClassVLCPlugin, kEventVLCPluginHideFullscreen);
         }
         else