macosx: Make supplementary view scroll views scroll parent scroll views once at end scroll position

This addresses the current behaviour where the supplementary library view scroll views absorb all scroll events, preventing the parent library scroll view from being scrolled when the mouse cursor is within the supplementary view scroll view

Screen_Recording_2022-08-31_at_19.22.21

Signed-off-by: Claudio Cambra claudio.cambra@gmail.com