Strife MAP10 compat fixes

[Rachael]

https://github.com/coelckers/gzdoom/pull/318

For review. This adds some code that I don't know exactly what it's doing, so it needs tested, but from my tests it worked fine.

[Graf Zahl]

Looks ok. What do you mean by 'don't know exactly what it's doing'?

[Rachael]

I've never used the SC parser before, and until now had no idea how it even worked. Adding in those fixes was mostly guessing and hoping that I got everything right.