Protect against line 335: TypeError: cnf.guru[obj.guru] is undefined

As reported in #synchronet by Android8675

exec/upgrade_to_v320.js

@@ -332,6 +332,7 @@ for(var i in cnf.chan) {
 	delete obj.code;
 	obj.actions = cnf.actset[obj.actset].name;
 	delete obj.actset;
+	if(cnf.guru[obj.guru])
 		obj.guru = cnf.guru[obj.guru].code;
 	ini.iniSetObject(key, obj);
 }