Removed "min_length" and "exact_length" from the list of rules that a…

…re run on empty fields, fixes #2809

classes/kohana/validate.php

@@ -440,7 +440,7 @@ public static function color($str)
 	protected $_labels = array();
 
 	// Rules that are executed even when the value is empty
-	protected $_empty_rules = array('not_empty', 'matches', 'min_length', 'exact_length');
+	protected $_empty_rules = array('not_empty', 'matches');
 
 	// Error list, field => rule
 	protected $_errors = array();