Fix width and separator of ToolButtonComplexControl outline w/ dropdown menu

Summary: Apparently, the code to adjust the rectangle when a menu is present is what was causing the problem. Also added an if statement to move the separator with the button when sunken.

Test Plan:
Old:

New:

Reviewers: VDG, Breeze, ngraham

Reviewed By: VDG, Breeze, ngraham

Subscribers: ngraham, plasma-devel

Tags: Plasma

Differential Revision: https://phabricator.kde.org/D23169