Make plasma panel visible again after disconnecting external display

I've been having this weird issue which is apparently known, but the workaround I got from https://bugs.kde.org/show_bug.cgi?id=356225 is below:

In $HOME/.config/plasma-org.kde.plasma.desktop-appletsrc there's a section "[Containments][1]". There within the option "lastScreen" often refers to the wrong screen, i.e. "1" instead of "0". When I change that option to "lastScreen=0" before starting the KDE session the panel is visible again on my laptop screen if it is the one and only available screen.

This is an important workaround because this panel not showing up on my laptop prevented my wifi from connecting and caused other odd behaviors.