(BF, BMD, SPD, PAK) Fix files not being emulated after initial creation

[AnimatedSwine37]

This fixes a bug that's present in BF, BMD, SPD, and PAK emulators that causes files to not be emulated if they are opened more than once (only the first creation works).

This is due to us using TryAdd in the _pathToEmulated concurrent dictionaries that should be used to pass back the previously emulated file when a file tries to be created subsequent times. It fails if something is already in the dictionary and since we put the value null in to prevent recursion, we end up with null even after emulation succeeds.

For simplicity I've just replaced TryAdd with a direct index (dict[thing]) instead of TryUpdate since I don't think concurrency is really a problem right now. Maybe this is something we need to consider more at some point but I'd guess that's a bigger problem?

[Sewer56]

Maybe this is something we need to consider more at some point but I'd guess that's a bigger problem?

You're expected to use these APIs during startup in general, so I think it's fine; the chances of concurrency issues there are pretty much for the most part, 0.