Fix clicking outside of preview popups to dismiss them corrupting mouse state

Summary:
As a result of refactorings in 5.10, hoveredItem may not reflect the
true cursor position when preview popups become involved. When inter-
acting with an item's associated preview popup, it's still considered
hovered. This needs to be taken into account when processing clicks,
otherwise corrupted mouse state leads e.g. to inadvertendly opening
a folder by clicking outside its preview popup to dismiss it.
BUG:380982

Reviewers: #plasma

Subscribers: broulik, plasma-devel

Tags: #plasma

Differential Revision: https://phabricator.kde.org/D6247