Possible fix for JX.History spookiness?

Summary: Ref T7573. I only got this reproducing like 10% of the time in Firefox but I can't reproduce it anymore after this change.

Test Plan:

• Added some logging.
• Saw Firefox handing us nonsense state values (?)
• Read the Firefox documentation?
• Maybe state is expected to be an object? This shouldn't matter?
• I don't really know?

Reviewers: btrahan

Reviewed By: btrahan

Subscribers: epriestley

Maniphest Tasks: T7573

Differential Revision: https://secure.phabricator.com/D12485