XQuartz: Only send mouse events while in the background if we're over a visible window.

This "breaks" xeyes but gets rid of annoying tooltips.
(cherry picked from commit 10090a132a0110fe24c8c886d9f53e6e947f8038)

hw/xquartz/X11Application.m

@@ -959,6 +959,22 @@ static void send_nsevent(NSEvent *e) {
                 pDev = darwinTabletCurrent;
             }
 
+            if(!quartzServerVisible) {
+                xp_window_id wid;
+                
+                /* Sigh. Need to check that we're really over one of
+                 * our windows. (We need to receive pointer events while
+                 * not in the foreground, and the only way to do that
+                 * right now is to ask for _all_ pointer events..)
+                 */
+                
+                wid = 0;
+                xp_find_window(pointer_x, pointer_y, 0, &wid);
+                
+                if (wid == 0)
+                    return;        
+            }
+            
             DarwinSendPointerEvents(pDev, ev_type, ev_button, pointer_x, pointer_y,
                                     pressure, tilt_x, tilt_y);