[effects/fallapart] Fix flickering problem

Summary:
The Fall Apart effect doesn't grab windows so a conflict could happen
if an alternative window open/close animation effect is enabled(e.g.
Fade, Glide).

### Before

{F5912324}

//Fall apart and Fade conflict with each other.//

### After

{F5912325}

//Only Fall apart animates the disappearing of System Settings.//

Test Plan:
* Enabled fall apart effect and fade effect
* Closed a window

Reviewers: #kwin, davidedmundson

Reviewed By: #kwin, davidedmundson

Subscribers: kwin

Tags: #kwin

Differential Revision: https://phabricator.kde.org/D13527