Snake: Ignore default keydown events

Before this patch, all key down events except arrow keys or WASD were
not propagated, so keyboard shortcuts in the application didn't work.

This patch fixes this :))

Userland/Games/Snake/SnakeGame.cpp

@@ -212,6 +212,7 @@ void SnakeGame::keydown_event(GUI::KeyEvent& event)
         queue_velocity(1, 0);
         break;
     default:
+        event.ignore();
         break;
     }
 }