am: fix broken email with --committer-date-is-author-date
Commit
e8cbe2118a (am: stop exporting GIT_COMMITTER_DATE, 2020-08-17)
rewrote the code for setting the committer date to use fmt_ident(),
rather than setting an environment variable and letting commit_tree()
handle it. But it introduced two bugs:
- we use the author email string instead of the committer email
- when parsing the committer ident, we used the wrong variable to
compute the length of the email, resulting in it always being a
zero-length string
This commit fixes both, which causes our test of this option via the
rebase "apply" backend to now succeed.
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>