Fixed incorrect case for _isValidSource() method call

Author: fballiano

lib/Varien/Io/File.php

@@ -496,7 +496,7 @@ public function write($filename, $src, $mode = null)
             throw new Exception('Detected malicious path or filename input.');
         }
 
-        if (!$this->_IsValidSource($src) || !$this->_isFilenameWriteable($filename)) {
+        if (!$this->_isValidSource($src) || !$this->_isFilenameWriteable($filename)) {
             return false;
         }