the first argument of updatePagePadding is expected to be a page, but when it is called from the throttledResize binding, it ends up as an event object, and the padding was being set on that instead of the page. This adds a check to ensure the arg is a page before setting its padding. This is a fix for #5619
Merge pull request #5826 from jquery/bug-5619-fixedtoolbarpadding

fix for 5619