fix off-by-one error in split_ident_line

Commit 4b340cfa split the logic to parse an ident line out of
pretty.c's format_person_part. But in doing so, it
accidentally introduced an off-by-one error that caused it
to think that single-character names were invalid.

This manifested itself as the "%an" format failing to show
anything at all for a single-character name.
Reported-by: NBrian Turner <bturner@atlassian.com>
Signed-off-by: NJeff King <peff@peff.net>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

ident.c

@@ -244,7 +244,7 @@ int split_ident_line(struct ident_split *split, const char *line, int len)
 	if (!split->mail_begin)
 		return status;
 
-	for (cp = split->mail_begin - 2; line < cp; cp--)
+	for (cp = split->mail_begin - 2; line <= cp; cp--)
 		if (!isspace(*cp)) {
 			split->name_end = cp + 1;
 			break;

t/t6006-rev-list-format.sh

@@ -282,4 +282,11 @@ test_expect_success 'oneline with empty message' '
 	test $(git rev-list --oneline --graph HEAD | wc -l) -eq 5
 '
 
+test_expect_success 'single-character name is parsed correctly' '
+	git commit --author="a <a@example.com>" --allow-empty -m foo &&
+	echo "a <a@example.com>" >expect &&
+	git log -1 --format="%an <%ae>" >actual &&
+	test_cmp expect actual
+'
+
 test_done