fixed bug with leaving scores screen on Android platform

fixed bug with leaving scores screen on Android platform

This change fixes a problem that occurs on the scores screen after
playing a game on Android, where the screen is left by any user input,
but then does not reset the flag that the last screen was the playing
screen, causing all other "choose tree" style screens to also exit on
any user input (which makes it impossible to select a different level
set on the level set selection screen afterwards, for example).