Some cleanup related to mt_rand()

- min and max values are 0 and mt_getrandmax() by default
- remove useless mt_srand() seed calls
diff --git a/system/libraries/Encrypt.php b/system/libraries/Encrypt.php
index c6a1cb1..8ac5420 100644
--- a/system/libraries/Encrypt.php
+++ b/system/libraries/Encrypt.php
@@ -244,7 +244,7 @@
 		$rand = '';
 		do
 		{
-			$rand .= mt_rand(0, mt_getrandmax());
+			$rand .= mt_rand();
 		}
 		while (strlen($rand) < 32);