`zlib.crc32_combine()` hangs on a negative length and `adler32_combine()` returns rubbish

[StanFromIreland]

Bug report

Bug description:

From the manual:

adler32_combine: If len2 is negative, the result has no meaning or utility.

crc32_combine: len2 must be non-negative.

To reproduce run:

$ python3.15 -c "import zlib; zlib.crc32_combine(0, 0, -5)"

which hangs due to a loop in zlib. And,

$ python3.15 -c "import zlib; print(zlib.adler32_combine(0, 0, -5))"
4294967295

which is rubbish.

CPython versions tested on:

CPython main branch

Operating systems tested on:

No response

Linked PRs

• gh-156180: Reject a negative len2 in zlib.{adler32,crc32}_combine() #156181
• [3.15] gh-156180: Reject a negative len2 in zlib.{adler32,crc32}_combine() (GH-156181) #156239