(minor) fix against crashes during certain console/debugging operations

When emptying DOM structure which still had a jQuery.wikibase.entityview, then inserting some
widget with toolbar again, we would most likely get an error by the entityview when entering
any edit mode. This is because events are still registered but the toolbar nodes do not have
their jQuery.data reference anymore. This has no practical usage in production but is useful
while debugging.

Change-Id: I7390e64616fd5597274d33182ba9902a9a03c800
Merge "(minor) fix against crashes during certain console/debugging operations"