[SystemTray] Fix item size for very narrow panel
Summary:
For very narrow panel item size is too big (item + padding exceed panel size). This adds a check to not exceed panel size.
Before:
After:
Test Plan:
- Make panel very narrow - icons should fit into panel
- Repeat for vertical/horizontal
Reviewers: Plasma: Workspaces, Plasma, ngraham, broulik
Reviewed By: ngraham
Subscribers: plasma-devel
Tags: Plasma
Differential Revision: https://phabricator.kde.org/D27958