Be more careful with user-supplied buffersrb/fix-2333

This adds in missing calls to `git_buf_sanitize` and fixes a
number of places where `git_buf` APIs could inadvertently write
NUL terminator bytes into invalid buffers.  This also changes the
behavior of `git_buf_sanitize` to NUL terminate a buffer if it can
and of `git_buf_shorten` to do nothing if it can.

Adds tests of filtering code with zeroed (i.e. unsanitized) buffer
which was previously triggering a segfault.

1 files changed, 3 insertions, 3 deletions

diff --git a/src/diff_print.c b/src/diff_print.c
index 07c1f8577..08e1e7f90 100644
--- a/src/diff_print.c
+++ b/src/diff_print.c
@@ -597,9 +597,9 @@ int git_diff_print_callback__to_file_handle(
 }
 
 /* print a git_patch to a git_buf */
-int git_patch_to_buf(
-	git_buf *out,
-	git_patch *patch)
+int git_patch_to_buf(git_buf *out, git_patch *patch)
 {
+	assert(out && patch);
+	git_buf_sanitize(out);
 	return git_patch_print(patch, git_diff_print_callback__to_buf, out);
 }