RangePick: Fix issue with range picker popup not opening

Created by: matthijskooijman

This popup is toggled using a button in the top bar of the overview window. There is some code in the on_focus_out event handler so the popup hides when it loses focus.

On some systems (observed on Debian Buster), the on_focus_out handler seems to trigger immediately after the popup is shown, causing it to be hidden again immediately, as reported in #639 (closed).

There is also some code in on_focus_out that detects when the focus is lost because the button was clicked, to prevent a situation where on_focus_out hides the popup and then the button click shows it again immediately.

Previously, in this situation on_focus_out would still hide the popup, but then prevent the next button click from showing it again. With this commit, this is reversed: on_focus_out does not hide the popup, instead relying on the button click to hide it instead.

This simplifies this special case a bit and ensures that the behavior from #639 (closed) no longer causes a problem (since the extra on_focus_out triggered by the initial click on the button now no longer hides the popup).

This fixes #639 (closed).