git-patch-id: do not trip over "no newline" markers

Currently, patch-id trips over our very own diff extension for marking
the absence of newline at EOF.

Fix it. (Ignore it, it's whitespace.)

Signed-off-by: Michael J Gruber <git@drmicha.warpmail.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/builtin/patch-id.c b/builtin/patch-id.c
index 5125300..49a0472 100644
--- a/builtin/patch-id.c
+++ b/builtin/patch-id.c
@@ -73,6 +73,8 @@
 			p += 7;
 		else if (!memcmp(line, "From ", 5))
 			p += 5;
+		else if (!memcmp(line, "\\ ", 2) && 12 < strlen(line))
+			continue;
 
 		if (!get_sha1_hex(p, next_sha1)) {
 			found_next = 1;