Fix memory leak of HotSpot

Summary:
Fixes memory leaf of HotSpots. This is caused by the Filter::reset()
function failing to delete the allocated HotSpots before clearing the
list.

Test Plan:
Compile konsole with address sanitizer
Select a link in the terminal
Close konsole

Reviewers: #konsole, hindenburg

Reviewed By: #konsole, hindenburg

Subscribers: hindenburg, konsole-devel

Tags: #konsole

Differential Revision: https://phabricator.kde.org/D19636