WebKit JSC arrayProtoFuncSplice Initialization Fail

WebKit: JSC: arrayProtoFuncSplice doesn't initialize all indices. CVE-2017-6980 Here's a snippet of arrayProtoFuncSplice. EncodedJSValue JSCHOSTCALL arrayProtoFuncSpliceExecState exec ... result = JSArray::tryCreateForInitializationPrivatevm,...