fixed handling "Escape" key on high score screen

Before, pressing the "Escape" key on the high score screen after
solving a level when using the game setting "auto-play next level"
started playing the next level.

Now, only "positive" input actions (like pressing "Space" or "Enter"
or pressing a joystick button) start playing the next level, while a
"negative" input action like pressing the "Escape" key always returns
to the main menu even with this game setting activated.