Chrome now fires extra popstate event on back, causing confirmLeave prompt to show twice

[Brikky]

Chrome browsers are bubbling up multiple popstate events, which causes the confirmLeave prompt box to show display twice when using the back/forward buttons.

The first time it's shown the dialog is passed an object with the page's location information, so the message is [Object object], the second dialog is the correct one generated by confirmLeave

This issue is caused because the DOMUtils don't anticipate this extra event in Chrome except on iOS. Changing this function to return true when the event state is undefined resolved this issue.

[ScriptedAlchemy]

Ill welcome a PR