checkdiff_consume: strtol parameter fix.

The second parameter is not the end of string input; it is
the optional return value to retrieve where the parser stopped.
Signed-off-by: NJunio C Hamano <junkio@cox.net>

diff.c

@@ -431,7 +431,7 @@ static void checkdiff_consume(void *priv, char *line, unsigned long len)
 	else if (line[0] == '@') {
 		char *plus = strchr(line, '+');
 		if (plus)
-			data->lineno = strtol(plus, line + len, 10);
+			data->lineno = strtol(plus, NULL, 10);
 		else
 			die("invalid diff");
 	}