In eventFilter() pass on to base class and only eat events when needed

Summary:
Clazy pointed out some overly greedy eventFilter() implementations.
No bugs uncovered by this, but feels better to not ignore possible needs of
base classes as well as other instances being interested in events.

Reviewers: KDevelop, kfunk

Reviewed By: KDevelop, kfunk

Subscribers: kfunk, kdevelop-devel

Differential Revision: https://phabricator.kde.org/D8990