popstate event always prevented for non-modal states

[zipper]

There is a problem for non-modal request, where AjaxModalExtension calls event.stopImmediatePropagation() for every non-modal state retrieved. Therefore no other popstate handlers will be run, even from other extensions or unrelated page scripts (if they were added after this callback).

Originally this event.stopImmediatePropagation() has been added for preventing extra request when closing modal which has been opened with data-naja-snippet-cache="off". In that case, there was an unnecessary request made.