[videoinfoscanner] re-use fasthash if possible

No need to compute a slow hash in case the fast one already succeeded. Same already happens for shows.

@jmarshallnz for review please.
I don't think that's easy to follow - way too many conditionals everywhere.

I suspect it might be easier if:

1. Drop bSkip=true, and the log from the fasthash match path.
2. Make the first if (!bSkip) and else (bSkip is now false anyway from 1).
3. Move the block beginning ln298 out of the condition from 2.

Thus, we have the "does it match" block first.

Then, we have a separate block below that compares the hashes, does the logging of the 4 cases, and sets bSkip appropriately.