use local copy of the json lib instead of include path

src/xml2json/xml2json.php

@@ -179,7 +179,8 @@ class xml2json {
 			}
 		} // End of if ($recursionDepth == 0) {		
 				
-		if (get_class($simpleXmlElementObject) == SIMPLE_XML_ELEMENT_PHP_CLASS) {
+		if (is_object($simpleXmlElementObject)
+			&& get_class($simpleXmlElementObject) == SIMPLE_XML_ELEMENT_PHP_CLASS) {
 			// Get a copy of the simpleXmlElementObject
 			$copyOfsimpleXmlElementObject = $simpleXmlElementObject;
       		// Get the object variables in the SimpleXmlElement object for us to iterate.