Fixed a bug in the upload library when allowed_files wasn't defined.
diff --git a/system/libraries/Upload.php b/system/libraries/Upload.php
index f804dce..33ee947 100644
--- a/system/libraries/Upload.php
+++ b/system/libraries/Upload.php
@@ -512,7 +512,7 @@
 	 */	

 	function is_allowed_filetype()

 	{

-		if (count($this->allowed_types) == 0)

+		if (count($this->allowed_types) == 0 || ! is_array($this->allowed_types))

 		{

 			$this->set_error('upload_no_file_types');

 			return FALSE;