Update the visiblity check for ActionToolbar by checking width with less-"equal".

Summary:
Otherwise some action, especially when there is only one action, it will be
put in "more" menu even if there is enough space.

Reviewers: Kirigami, mart, ngraham

Reviewed By: Kirigami, ngraham

Subscribers: ngraham, plasma-devel

Tags: Kirigami

Differential Revision: https://phabricator.kde.org/D29022