ClippableElement: Compatibility with jQuery 3
ClippableElement: Compatibility with jQuery 3

We were relying on the jQuery 1 behavior where `$( window ).offset()`
returns undefined. In jQuery 3, it throws an exception. Explicitly
check for this case instead.

Bug: T152778
Change-Id: Ib911153f348fedf1f469b50330009fec810394ac

wikimedia/oojs-ui,wikimedia/oojs-ui,wikimedia/oojs-ui,wikimedia/oojs-ui