AGOS: Added detection for Simon the Sorcerer 1 CD32 demo

I have verified that the demo is completable, though it doesn't
actually seems to end. You're just told that there is nothing more
for you to do.
AGOS: Fix invisibility in Amiga CD32 Simon the Sorcerer 1 demo

This probably affects the full version as well, but I haven't
verified that. Either way, the old code was obviously wrong while
the new makes it look right to me.
Merge https://github.com/scummvm/scummvm