api.new.get.thread_data() no longer works with domThread object.

[josteink]

Demonstrated through the following snippet:

gmail.observe.on("view_thread", (domThread) => {
    console.log("Looking at thread:", domThread);
    const threadData = gmail.new.get.thread_data(domThread);
    console.log("Thread data:", threadData); // reports null!
}

[josteink]

Fixed. Closing.