Ensure _checkDupOffset() doesn't remove the wrong duplicate

[dwatteau]

Note to myself: I need to make sure that _checkDupOffset() doesn't remove the wrong duplicate when it finds one. Otherwise the game could be playable, until an internal script error happens under some particular circumstances…

Ideas on how to check this:

• Check against other variants not having the bug (other platforms, other languages…)
• Try reading the scripts through descumm
• Use another SCUMM resource explorer

[dwatteau]

The current workarounds look OK, although I didn't do any 100% thorough gameplay of them after the duplicates are removed. For my workaround addition to Loom in particular, removing the other duplicate does crash the game, so yeah it looks good the way it is (and that's how I stumbled upon issue #45).

My only doubt is in the MONKEY1-FLOPPY-VGA I introduced in commit dc94b2a, but anyway it had to be disabled for the ScummTR 0.5.0 release, because of the #47 bug.

So let's close this.