Fix to to_csv() for determining if data is a multi-dimensional array

Author: Kevin Wood-Friend

application/libraries/Format.php

@@ -185,7 +185,7 @@ public function to_csv()
 		$data = $this->_data;
 
 		// Multi-dimensional array
-		if (isset($data[0]))
+		if (isset($data[0]) && is_array($data[0]))
 		{
 			$headings = array_keys($data[0]);
 		}