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/screen.h

@@ -73,6 +73,13 @@ screen_init(struct screen *screen, struct fps_counter *fps_counter,
 void
 screen_destroy(struct screen *screen);
 
+// hide the window
+//
+// It is used to hide the window immediately on closing without waiting for
+// screen_destroy()
+void
+screen_hide_window(struct screen *screen);
+
 // render the texture to the renderer
 //
 // Set the update_content_rect flag if the window or content size may have