Fix hang on Skia/Win when we press the HWND close button and an ui::Alert is shown

We don't have to close the OS window when its close button is pressed.
We just generate an CloseDisplay event and the client (app/ui layer) must
process it (e.g. check if there are no unsaved changes) and then close
the she::Display manually.

src/she/win/window.h

@@ -234,7 +234,10 @@ namespace she {
           Event ev;
           ev.setType(Event::CloseDisplay);
           queueEvent(ev);
-          break;
+
+          // Don't close the window, it must be closed manually after
+          // the CloseDisplay event is processed.
+          return 0;
         }
 
         case WM_PAINT: {