Make sure to animate proper containments

Summary:
if the activity is changed again while the switch animation
is being performed, the desktop finds itself in an
inconsistent state, as oldContainment and newContainment
values gets changed while the animation is running.
this makes sure the animation is stopped and all the values
are resetted if the containment changes before the anim is done

BUG:352345

Test Plan: tried with the animation made really slow, was easy to reproduce 352345, then the problem went away with the patch

Reviewers: Plasma, davidedmundson

Reviewed By: Plasma, davidedmundson

Subscribers: plasma-devel

Tags: Plasma

Differential Revision: https://phabricator.kde.org/D2814