Fix search result rectangle position

Summary:
Include top margin in the rectangle's vertical position, so it will
be drawn in correct position when TerminalCenter is set and/or
TerminalMargin is larget than 0.

Preview:
{F5756612}

Test Plan:
  - Run `konsole -p TerminalMargin=8`
  - Display something
  - Run search and search for something
  - The blue rectangle should cover current result line

Reviewers: #konsole, hindenburg

Reviewed By: #konsole, hindenburg

Subscribers: hindenburg, #konsole

Tags: #konsole

Differential Revision: https://phabricator.kde.org/D11412