gc: fix off-by-one error with gc.autoPackLimit

This matches the documentation and allows gc.autoPackLimit=1
to maintain a single pack without attempting a repack on every
"git gc --auto" invocation.

Signed-off-by: Eric Wong <e@80x24.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/gc.c

@@ -145,7 +145,7 @@ static int too_many_packs(void)
 		 */
 		cnt++;
 	}
-	return gc_auto_pack_limit <= cnt;
+	return gc_auto_pack_limit < cnt;
 }
 
 static void add_repack_all_option(void)