revert: simplify getting commit subject in format_todo()

format_todo() calls get_message(), but uses only the subject line of
the commit message.  As a minor optimization, save work and
unnecessary memory allocations by using find_commit_subject() instead.
Also, remove the unnecessary check on cur->item->buffer: the
lookup_commit_reference() call in parse_insn_line() has already made
sure of this.

Suggested-by: Jonathan Nieder <jrnieder@gmail.com>
Helped-by: Junio C Hamano <gitster@pobox.com>
Signed-off-by: Ramkumar Ramachandra <artagnon@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/revert.c

@@ -700,16 +700,16 @@ static int format_todo(struct strbuf *buf, struct commit_list *todo_list,
 		struct replay_opts *opts)
 {
 	struct commit_list *cur = NULL;
-	struct commit_message msg = { NULL, NULL, NULL, NULL, NULL };
 	const char *sha1_abbrev = NULL;
 	const char *action_str = opts->action == REVERT ? "revert" : "pick";
+	const char *subject;
+	int subject_len;
 
 	for (cur = todo_list; cur; cur = cur->next) {
 		sha1_abbrev = find_unique_abbrev(cur->item->object.sha1, DEFAULT_ABBREV);
-		if (get_message(cur->item, &msg))
-			return error(_("Cannot get commit message for %s"), sha1_abbrev);
-		strbuf_addf(buf, "%s %s %s\n", action_str, sha1_abbrev, msg.subject);
-		free_message(&msg);
+		subject_len = find_commit_subject(cur->item->buffer, &subject);
+		strbuf_addf(buf, "%s %s %.*s\n", action_str, sha1_abbrev,
+			subject_len, subject);
 	}
 	return 0;
 }