Cygwin/X: Ignore MappingNotify events sent to clipboard integration client

Ignore MappingNotify events sent to clipboard integration client,
xmodmap changes aren't of interest to it, but there is no mechanism
to express that disinterest.

Signed-off-by: Jon TURNEY <jon.turney@dronecode.org.uk>
Reviewed-by: Colin Harrison <colin.harrison@virgin.net>

hw/xwin/winclipboardxevents.c

@@ -789,6 +789,9 @@ winClipboardFlushXEvents (HWND hwnd,
 	case PropertyNotify:
 	  break;
 
+	case MappingNotify:
+	  break;
+
 	default:
           ErrorF ("winClipboardFlushXEvents - unexpected event type %d\n", event.type);
 	  break;