fix(modal): check for overflow hidden

[RobJacobs]

Check if appendToElement has scrolling disabled before adding
the scrollbar padding.

Fixes #6037

[icfantv]

LGTM

[phazei]

This "fix" actually breaks the padding added in every other case. It only checks the elements parent is scrollable, but the way it does the check, via visibility, fails for the body tag, since overflow is always 'visible' but it still produces scrollbars. I'm not familiar with any case where the element isn't appended to the body, so I don't know what happens there, but in the default case, this breaks generall use so should be rolled back.