git-mailinfo: Fix getting the subject from the in-body [PATCH] line

"Subject: " isn't in the static array "header", and thus
memcmp("Subject:", header[i], 7) will never match.

Even if it did so, hdr_data[] may not have been allocated if there weren't
a "Subject: " in-body when we process "[PATCH]" in the affected codepath.

Signed-off-by: Lukas Sandström <lukass@etek.chalmers.se>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/t/t5100/patch0010 b/t/t5100/patch0010
new file mode 100644
index 0000000..f055481
--- /dev/null
+++ b/t/t5100/patch0010
@@ -0,0 +1,20 @@
+---
+ builtin-mailinfo.c |    2 +-
+ 1 files changed, 1 insertions(+), 1 deletions(-)
+
+diff --git a/builtin-mailinfo.c b/builtin-mailinfo.c
+index 962aa34..2d1520f 100644
+--- a/builtin-mailinfo.c
++++ b/builtin-mailinfo.c
+@@ -334,7 +334,7 @@ static int check_header(char *line, unsigned linesize, char **hdr_data, int over
+ 		return 1;
+ 	if (!memcmp("[PATCH]", line, 7) && isspace(line[7])) {
+ 		for (i = 0; header[i]; i++) {
+-			if (!memcmp("Subject: ", header[i], 9)) {
++			if (!memcmp("Subject", header[i], 7)) {
+ 				if (! handle_header(line, hdr_data[i], 0)) {
+ 					return 1;
+ 				}
+-- 
+1.5.6.2.455.g1efb2
+