ws: Do not block on wl_event_loop_dispatch()

Instruct wl_display_get_event_loop() to not block by passing
zero as timeout, instead of letting it block indefinitely.

Fixes #94

(cherry picked from commit d3b5da7)

src/ws.cpp

@@ -117,7 +117,7 @@ GSourceFuncs ServerSource::s_sourceFuncs = {
 
         if (source.pfd.revents & G_IO_IN) {
             struct wl_event_loop* eventLoop = wl_display_get_event_loop(source.display);
-            wl_event_loop_dispatch(eventLoop, -1);
+            wl_event_loop_dispatch(eventLoop, 0);
             wl_display_flush_clients(source.display);
         }