Precomp v0.4.8 Neo v0.4.1a

No big highlight feature this time, just bugfixes.

• Fix for rare crash where Preflate would try to read past it's input data causing failures and crashes
  • As such this bug doesn't actually have to do with Precomp itself, and was present since mainline Precomp v0.4.8 (or earlier)
  • It's a very rudimentary fix that doesn't really get to the bottom of the issue, but at least prevents the crashes
• This one is fully on me: Fix for some single IDAT PNG files not being properly precompressed, that would precompress fine on Precomp v0.4.8, due to a bug introduced during Precomp Neo refactoring
• Fix some errors in memiostreams code, which I don't know if they were actually causing any issues, but the code was nonetheless corrected

I think this, in addition to verification added on Precomp Neo 0.4a previously, get us to a point where crashes, complete hangs or bad data should be very rare, so I consider this a milestone in terms of stability.
There are still problems related with specific formats and slowdowns and the like, and of course I don't assume we won't find any more issues in the future, but for now, most of the egregious problems seem to have been solved... I hope