... if that toolbox is in popup mode (e.g. shapes toolbar
dropdowns, or the toolbar overflow floater). Same behavior
was introduced for non menu based dropdowns in
81d4fbc0 ("tdf#42029 Use a
floating toolbar to show clipped items"), and is similar
to what we had already in ToolBox::Select, i.e. when the
user made a selection, the floating windows should close.

This must be done before executing the menu selection
handler, because such handler might execute stuff
synchronously (e.g. MenuBarManager::Select), and if it
will open a modal dialog, the floating toolbox will stay
visible after the dialog shows.

Change-Id: Ie93e71fa4dea80ba444aebccacf6adb926a39224