FilterList.apply_to_* truncate output at the first NUL byte #1507

FilterList.apply_to_buffer, apply_to_file and apply_to_blob return ffi.string(buf.ptr), which stops at the first NUL byte, so binary data comes back truncated.

It shows up for any binary file that gets a filter list, e.g. with core.autocrlf=true or * text=auto in .gitattributes. The crlf filter passes binary data through unchanged, and pygit2 then cuts it at the first NUL:

import tempfile

import pygit2

repo = pygit2.init_repository(tempfile.mkdtemp())
repo.config['core.autocrlf'] = True
fl = repo.load_filter_list('image.png')
data = b'\x89PNG\r\n\x1a\n\x00\x00\x00\rIHDR'
print(fl.apply_to_buffer(data))  # b'\x89PNG\r\n\x1a\n'

Seen in 1.19.2 through 1.21.0 (libgit2 1.9.7). In GitFourchette, the preview of an unstaged image in such a repo shows "0 × 0 pixels, 8 bytes".

Reading the buffer with its length fixes it: ffi.buffer(buf.ptr, buf.size)[:] in all three methods. With that change and a test that runs NUL bytes through all three, the suite passes (677 passed, 6 skipped). I can open a PR if you'd like.

Repository.raw_message (repository.py:1298) has the same ffi.string(buf.ptr) and cuts MERGE_MSG at a NUL. That one hardly matters, since git refuses to commit a message containing NUL.

Prepared with Claude Code; I reviewed the changes.