Remove useless screen render on initialization

screen_render() should not be called on initialization:
 1. it is useless, since the window is hidden until the first frame;
 2. it writes an empty texture (probably green) to the renderer.

app/src/screen.c

@@ -173,7 +173,6 @@ SDL_bool screen_init_rendering(struct screen *screen, const char *device_name, s
         return SDL_FALSE;
     }
 
-    screen_render(screen);
     return SDL_TRUE;
 }