rebase: fix broken email with --committer-date-is-author-date

Commit 7573cec52c (rebase -i: support --committer-date-is-author-date,
2020-08-17) copied the committer ident-parsing code from builtin/am.c.
And in doing so, it copied a bug in which we always set the email to an
empty string. We fixed the version in git-am in the previous commit;
this commit fixes the copied code.

Reported-by: VenomVendor <info@venomvendor.com>
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

sequencer.c

@@ -4369,7 +4369,7 @@ static int init_committer(struct replay_opts *opts)
 	opts->committer_name =
 		xmemdupz(id.name_begin, id.name_end - id.name_begin);
 	opts->committer_email =
-		xmemdupz(id.mail_begin, id.mail_end - id.mail_end);
+		xmemdupz(id.mail_begin, id.mail_end - id.mail_begin);
 
 	return 0;
 }

t/t3436-rebase-more-options.sh

@@ -76,20 +76,20 @@ test_expect_success '--committer-date-is-author-date works with apply backend' '
 	test_ctime_is_atime -1
 '
 
-test_expect_failure '--committer-date-is-author-date works with merge backend' '
+test_expect_success '--committer-date-is-author-date works with merge backend' '
 	GIT_AUTHOR_DATE="@1234 +0300" git commit --amend --reset-author &&
 	git rebase -m --committer-date-is-author-date HEAD^ &&
 	test_ctime_is_atime -1
 '
 
-test_expect_failure '--committer-date-is-author-date works with rebase -r' '
+test_expect_success '--committer-date-is-author-date works with rebase -r' '
 	git checkout side &&
 	GIT_AUTHOR_DATE="@1234 +0300" git merge --no-ff commit3 &&
 	git rebase -r --root --committer-date-is-author-date &&
 	test_ctime_is_atime
 '
 
-test_expect_failure '--committer-date-is-author-date works when forking merge' '
+test_expect_success '--committer-date-is-author-date works when forking merge' '
 	git checkout side &&
 	GIT_AUTHOR_DATE="@1234 +0300" git merge --no-ff commit3 &&
 	PATH="./test-bin:$PATH" git rebase -r --root --strategy=test \
@@ -145,7 +145,7 @@ test_expect_success '--reset-author-date works with rebase -r' '
 	test_atime_is_ignored
 '
 
-test_expect_failure '--reset-author-date with --committer-date-is-author-date works' '
+test_expect_success '--reset-author-date with --committer-date-is-author-date works' '
 	test_must_fail git rebase -m --committer-date-is-author-date \
 		--reset-author-date --onto commit2^^ commit2^ commit3 &&
 	git checkout --theirs foo &&