bisect: avoid signed integer overflow

Signed-off-by: John Keeping <john@keeping.me.uk>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

bisect.c

@@ -525,9 +525,9 @@ struct commit_list *filter_skipped(struct commit_list *list,
  * is increased by one between each call, but that should not matter
  * for this application.
  */
-static int get_prn(int count) {
+static unsigned get_prn(unsigned count) {
 	count = count * 1103515245 + 12345;
-	return ((unsigned)(count/65536) % PRN_MODULO);
+	return (count/65536) % PRN_MODULO;
 }
 
 /*