[PATCH] git-rev-list: avoid crash on broken repository

When following tags, check for parse_object() success and error out
properly instead of segfaulting.

Signed-off-by: Sergey Vlasov <vsu@altlinux.ru>
Signed-off-by: Junio C Hamano <junkio@cox.net>

rev-list.c

@@ -418,6 +418,8 @@ static struct commit *get_commit_reference(const char *name, unsigned int flags)
 		if (tag_objects && !(object->flags & UNINTERESTING))
 			add_pending_object(object, tag->tag);
 		object = parse_object(tag->tagged->sha1);
+		if (!object)
+			die("bad object %s", sha1_to_hex(tag->tagged->sha1));
 	}
 
 	/*