[libzstd] Fix infinite loop in decompression

When we switched `ZSTD_SKIPPABLEHEADERSIZE` to a macro, the places where we do:

    MEM_readLE32(ptr) + ZSTD_SKIPPABLEHEADERSIZE

can now overflow `(unsigned)-8` to `0` and we infinite loop. We now check
the frame size and reject sizes that overflow a U32.

Note that this bug never made it into a release, and was only in the dev branch
for a few days.

Credit to OSS-Fuzz