Merge branch 'tb/repack-cleanup'

The recent change to "git repack" made it react less nicely when a
leftover .idx file that no longer has the corresponding .pack file
in the repository, which has been corrected.

* tb/repack-cleanup:
  builtin/repack.c: avoid dir traversal in `collect_pack_filenames()`
  builtin/repack.c: only repack `.pack`s that exist

diff --cc builtin/repack.c
Simple merge