Hide the window immediately on close

The screen may not be destroyed immediately on close to avoid undefined
behavior, because it may still receive events from the decoder.

But the visual window must still be closed immediately.

app/src/scrcpy.c

@@ -398,6 +398,10 @@ scrcpy(const struct scrcpy_options *options) {
     ret = event_loop(options);
     LOGD("quit...");
 
+    // Close the window immediately on closing, because screen_destroy() may
+    // only be called once the stream thread is joined (it may take time)
+    screen_hide_window(&screen);
+
 end:
     // The stream is not stopped explicitly, because it will stop by itself on
     // end-of-stream