Fix XMLHttpRequest for Node Runtime

[dragonlobster]

If using this JS SDK without the browser, XMLHttpRequest won't exist - therefore this error occurs:

const descriptor = Object.getOwnPropertyDescriptor(XMLHttpRequest.prototype, "withCredentials");
                                                     ^
ReferenceError: XMLHttpRequest is not defined

In order to fix this we should check if XMLHttpRequest exists first before.

[CLAassistant]

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