builtin/blame: fix out-of-bounds read with excessive `--abbrev`

In 6411a0a896 (builtin/blame: fix type of `length` variable when emitting object ID, 2024-12-06) we have fixed the type of the `length` variable. In order to avoid a cast from `size_t` to `int` in the call to printf(3p) with the "%.*s" formatter we have converted the code to instead use fwrite(3p), which accepts the length as a `size_t`. It was reported though that this makes us read over the end of the OID array when the provided `--abbrev=` length exceeds the length of the object ID. This is because fwrite(3p) of course doesn't stop when it sees a NUL byte, whereas printf(3p) does. Fix the bug by reverting back to printf(3p) and culling the provided length to `GIT_MAX_HEXSZ` to keep it from overflowing when cast to an `int`. Reported-by: Johannes Schindelin <Johannes.Schindelin@gmx.de> Signed-off-by: Patrick Steinhardt <ps@pks.im> Signed-off-by: Junio C Hamano <gitster@pobox.com>