Player: Crash on unhandled empty cancel option in Show Choice command

[fdelapena]

If some game uses an empty option as selected on empty cancel, Player will crash. The following screenshot shows how the cancel key action is mapped to the empty 3rd option:

RPG_RT.exe seems to fallback to Cancel and does not display any error, continuing the game as usual.

[Ghabry]

we really lack sanity checks all around the interpreter but not worth implementing them everywhere before the magic number code smell is resolved (there was a liblcf issue for thsi, can't findi t)

But this one should be simple to fix.

[Ghabry]

I think we catched a common Android crash here 👍

Affected 47 users over the last 60 days.

(is always hard to tell what the real cause is based on the stacktrace)