sequencer: use skip_blank_lines() to find the commit subject

Just like we already taught the find_commit_subject() function (to make
it consistent with the code in pretty.c), we now simply skip leading
blank lines of the commit message.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

sequencer.c

@@ -568,10 +568,8 @@ static int do_pick_commit(struct commit *commit, struct replay_opts *opts)
 		 * information followed by "\n\n".
 		 */
 		p = strstr(msg.message, "\n\n");
-		if (p) {
+		if (p)
-			p += 2;
+			strbuf_addstr(&msgbuf, skip_blank_lines(p + 2));
-			strbuf_addstr(&msgbuf, p);
-		}
 
 		if (opts->record_origin) {
 			if (!has_conforming_footer(&msgbuf, NULL, 0))