ActionToolBar: Only show the overflow button if there are visible items in the menu
Summary:
This fixes https://bugs.kde.org/show_bug.cgi?id=415412 , which was occuring because the
overflow button did not properly check to see if the actions in the menu were actually
visible.
BUG: 415412
Test Plan: The example code from the linked bug report now works correctly.
Reviewers: Kirigami, ngraham, apol
Reviewed By: Kirigami, ngraham, apol
Subscribers: apol, ngraham, plasma-devel
Tags: Kirigami
Differential Revision: https://phabricator.kde.org/D26279