builtin-apply.c: optimize match_beginning/end processing a bit.

Wnen the caller knows the hunk needs to match at the beginning
or at the end, there is no point starting from the line number
that is found in the patch and trying match with increasing
offset.  The logic to find matching lines was made more line
oriented with the previous patch and this optimization is now
trivial.

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

builtin-apply.c

@@ -1579,6 +1579,16 @@ static int find_pos(struct image *img,
 	if (preimage->nr > img->nr)
 		return -1;
 
+	/*
+	 * If match_begining or match_end is specified, there is no
+	 * point starting from a wrong line that will never match and
+	 * wander around and wait for a match at the specified end.
+	 */
+	if (match_beginning)
+		line = 0;
+	else if (match_end)
+		line = img->nr - preimage->nr;
+
 	try = 0;
 	for (i = 0; i < line; i++)
 		try += img->line[i].len;