git-zlib: handle data streams larger than 4GB

git-zlib: handle data streams larger than 4GB

On Windows, zlib's `uLong` type is 32-bit even on 64-bit systems. When
processing data streams larger than 4GB, the `total_in` and `total_out`
fields in zlib's `z_stream` structure wrap around, which caused the
sanity checks in `zlib_post_call()` to trigger `BUG()` assertions.

The git_zstream wrapper now tracks its own 64-bit totals rather than
copying them from zlib. The sanity checks compare only the low bits,
using `maximum_unsigned_value_of_type(uLong)` to mask appropriately for
the platform's `uLong` size.

This is based on work by LordKiRon in git-for-windows#6076.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>