Merge branch 'sa/multi-mailmap-fix' into next

When asking to apply mailmap to both author and committer field
while showing a commit object, the field that appears later was not
correctly parsed and replaced, which has been corrected.

* sa/multi-mailmap-fix:
  cat-file: fix mailmap application for different author and committer

diff --cc ident.c
Simple merge

diff --cc t/t4203-mailmap.sh
Simple merge