apply: do not barf on patch with too large an offset

Previously a patch that records too large a line number caused the
offset matching code in git-apply to overstep its internal buffer.

Noticed by Johannes Schindelin.

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

builtin-apply.c

@@ -1809,6 +1809,9 @@ static int find_pos(struct image *img,
 	else if (match_end)
 		line = img->nr - preimage->nr;
 
+	if (line > img->nr)
+		line = img->nr;
+
 	try = 0;
 	for (i = 0; i < line; i++)
 		try += img->line[i].len;