Display dialog goes haywire after unplugging an external monitor

Submitted by Yousuf Philips @philipzae

Assigned to Xfce Bug Triage

Link to original bug (#16729)

Description

Steps:

1. startup with an external monitor
2. open up display dialog
3. unplug external monitor
4. dialog shows to headers and UI elements are missing until hovering over them

Tested on Xubuntu 19.10

Version: 4.14.1