Ignore leading empty lines while summarizing merges

"git log" and friends normally skip the initial empty lines when showing
one-line summary of a commit, but merge summary didn't.

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
----
 builtin-fmt-merge-msg.c |   10 +++++++++-
 1 files changed, 9 insertions(+), 1 deletions(-)

Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin-fmt-merge-msg.c

@@ -200,14 +200,22 @@ static void shortlog(const char *name, unsigned char *sha1,
 			continue;
 
 		bol = strstr(commit->buffer, "\n\n");
+		if (bol) {
+			unsigned char c;
+			do {
+				c = *++bol;
+			} while (isspace(c));
+			if (!c)
+				bol = NULL;
+		}
+
 		if (!bol) {
 			append_to_list(&subjects, xstrdup(sha1_to_hex(
 							commit->object.sha1)),
 					NULL);
 			continue;
 		}
 
-		bol += 2;
 		eol = strchr(bol, '\n');
 		if (eol) {
 			oneline = xmemdupz(bol, eol - bol);