Report video buffer downstream errors

Make the video buffer stop if its consumer could not receive a frame.

app/src/screen.h

@@ -59,8 +59,6 @@ struct sc_screen {
     bool maximized;
     bool mipmaps;
 
-    bool event_failed; // in case SDL_PushEvent() returned an error
-
     // To enable/disable mouse capture, a mouse capture key (LALT, LGUI or
     // RGUI) must be pressed. This variable tracks the pressed capture key.
     SDL_Keycode mouse_capture_key_pressed;