quartz: fix a race condition when waking up the CGRunLoop

Wake up the run loop unconditionally (don't check if it is waiting) because
it might go into waiting state right after we checked for it. Fixes GIMP
startup (which has a lot of GIOChannel I/O but zero NSEvents) from several
minutes to a few seconds.
(cherry picked from commit 0729cdc9a1)

gdk/quartz/gdkeventloop-quartz.c

@@ -207,9 +207,12 @@ signal_main_thread (void)
    */
   if (!run_loop_polling_async)
     CFRunLoopSourceSignal (select_main_thread_source);
-  
-  if (CFRunLoopIsWaiting (main_thread_run_loop))
-    CFRunLoopWakeUp (main_thread_run_loop);
+
+  /* Don't check for CFRunLoopIsWaiting() here because it causes a
+   * race condition (the loop could go into waiting state right after
+   * we checked).
+   */
+  CFRunLoopWakeUp (main_thread_run_loop);
 }
 
 static void *