:bug: Fix buttons not being released on Android
:bug: Fix buttons not being released on Android

To check if a button had a touch identifier assigned, I was negating the
identifier `if (!identifier) {`. Which doesn't behave as indented when
the identifier is `0`. Android happens to assign identifiers for any
available number starting from 0.

dasilvacontin/ludumpad-client,dasilvacontin/ludumpad,dasilvacontin/ludumpad