Merge branch 'ps/missing-btmp-fix'

GIt 2.44 introduced a regression that makes the updated code to
barf in repositories with multi-pack index written by older
versions of Git, which has been corrected.

* ps/missing-btmp-fix:
  pack-bitmap: gracefully handle missing BTMP chunks

diff --cc midx.c
Simple merge

diff --cc pack-bitmap.c
Simple merge