custom pretty format: tolerate empty e-mail address

When e-mail address is empty (e.g. "A U Thor <>"), --pretty=format
misparsed the commit header and did not pick up the date field correctly.

Noticed by Marco, fixed slightly differently with additional sanity
check and with a test.
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

pretty.c

@@ -292,7 +292,18 @@ static void format_person_part(struct strbuf *sb, char part,
 	/* parse name */
 	for (end = 0; end < len && msg[end] != '<'; end++)
 		; /* do nothing */
+	/*
+	 * If it does not even have a '<' and '>', that is
+	 * quite a bogus commit author and we discard it;
+	 * this is in line with add_user_info() that is used
+	 * in the normal codepath.  When end points at the '<'
+	 * that we found, it should have matching '>' later,
+	 * which means start (beginning of email address) must
+	 * be strictly below len.
+	 */
 	start = end + 1;
+	if (start >= len - 1)
+		return;
 	while (end > 0 && isspace(msg[end - 1]))
 		end--;
 	if (part == 'n') {	/* name */
@@ -300,11 +311,8 @@ static void format_person_part(struct strbuf *sb, char part,
 		return;
 	}
 
-	if (start >= len)
-		return;
-
 	/* parse email */
-	for (end = start + 1; end < len && msg[end] != '>'; end++)
+	for (end = start; end < len && msg[end] != '>'; end++)
 		; /* do nothing */
 
 	if (end >= len)

t/t6006-rev-list-format.sh

@@ -139,4 +139,14 @@ commit 131a310eb913d107dd3c09a65d1651175898735d
 commit 86c75cfd708a0e5868dc876ed5b8bb66c80b4873
 EOF
 
+test_expect_success 'empty email' '
+	test_tick &&
+	C=$(GIT_AUTHOR_EMAIL= git commit-tree HEAD^{tree} </dev/null) &&
+	A=$(git show --pretty=format:%an,%ae,%ad%n -s $C) &&
+	test "$A" = "A U Thor,,Thu Apr 7 15:14:13 2005 -0700" || {
+		echo "Eh? $A" >failure
+		false
+	}
+'
+
 test_done