commit-graph: avoid memory leaks

commit-graph: avoid memory leaks

A fuzzer running on the entry point provided by fuzz-commit-graph.c
revealed a memory leak when parse_commit_graph() creates a struct
bloom_filter_settings and then returns early due to error. Fix that
error by always freeing that struct first (if it exists) before
returning early due to error.

While making that change, I also noticed another possible memory leak -
when the BLOOMDATA chunk is provided but not BLOOMINDEXES. Also fix that
error.

Signed-off-by: Jonathan Tan <jonathantanmy@google.com>
Reviewed-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>