csum-file: always finalize or discard hash

When a hashfile struct is created, we always initialize the git_hash_ctx inside it. We usually end up in hashfile_finalize(), which passes that ctx to git_hash_final(), cleaning it up. But a few code paths don't do so: 1. If we bail on the hashfile and call free_hashfile() directly rather than finalizing. 2. If the skip_hash flag is set, the hashfile_finalize() call will never call git_hash_final(). (You might think that we should just avoid git_hash_init() entirely in this case, but the skip_hash flag is set by the caller after the hashfile is initialized). For most hash implementations this is OK, but for ones that allocate on initialization it causes a memory leak. You can see many failures by running: make SANITIZE=leak OPENSSL_SHA1_UNSAFE=1 test since OpenSSL >= 3.0 is such an allocating hash implementation (and csum-file uses the "unsafe" algorithm variant). We can solve this by calling git_hash_discard() as appropriate. Note that free_hashfile() is used both directly by callers to abort without finalizing, and by hashfile_finalize() to free memory. In the latter case we _don't_ want to call git_hash_discard(), because we'll already have either finalized or discarded it. So we'll push that to an internal "free_memory" function, and keep free_hashfile() as the public interface to abort a hashfile without finalizing. This fix makes several scripts leak-free with the command above: t1600, t1601, t2107, t7008, t9210, t9211. Signed-off-by: Jeff King <peff@peff.net> Signed-off-by: Junio C Hamano <gitster@pobox.com>