Fixup Perseus.fixupJSON

Summary:
I forgot to send an initial state to the editor in fixupJSON. That'll
teach me to not test the empty case in future test plans...

Test Plan:
run

    Perseus.fixupJSON({question: {content: "hi"}}).then(function(j) {
        console.log(JSON.stringify(j.question)); });

check that it prints

    {"content":"hi","images":{},"widgets":{}}

Auditors: joel