Lock screen not work properly when second monitor unplugged during hibernation.

Maybe related to:
#129
#111
xfce/xfce4-power-manager#68

Tested on 4.18.2 - openSUSE Tumbleweed

After unplugging main display and waking from hibernation, lock screen is not fully active. Desktop and opened windows are visible, it's not frozen screen because notifications also work but nothing can be clicked with mouse and keyboard also seems to do nothing.

Reproduce steps:

1. Plug two displays to computer
2. Set one of them as main
3. Enable following settings:
   • Screensaver Preferences -> Screensaver -> "Activate screensaver when computer is idle"
   • Screensaver Preferences -> Lock screen -> "Enable screen lock"
   • Screensaver Preferences -> Lock screen -> "Lock screen on screensaver"
   • Screensaver Preferences -> Lock screen -> "Lock screen on system sleep"
   • Power Manager -> System -> "Lock screen on system halt"
   • Session and Startup -> General -> "Lock screen before sleep"
4. Hibernate system
5. Unplug main display
6. Wake up system
7. You should see desktop and active windows on second display
8. Connect back main display
9. Lock screen should activate (can be weirdly stretcher but will work)

Log from .xsession-errors:

** (process:14551): WARNING **: 19:49:38.433: /etc/pam.d/xfce4-screensaver does not exist.
Authentication via PAM is unlikely to work.

(xfce4-notifyd:1972): xfce4-notifyd-WARNING **: 19:49:45.571: Failed to truncate DB: column index out of range

** (process:14941): WARNING **: 19:50:18.399: /etc/pam.d/xfce4-screensaver does not exist.
Authentication via PAM is unlikely to work.

(xfce4-power-manager-settings:15342): Gtk-CRITICAL **: 19:52:08.290: gtk_widget_hide: assertion 'GTK_IS_WIDGET (widget)' failed

(xfce4-power-manager-settings:15342): Gtk-CRITICAL **: 19:52:08.290: gtk_widget_hide: assertion 'GTK_IS_WIDGET (widget)' failed

** (process:16156): WARNING **: 19:54:48.956: /etc/pam.d/xfce4-screensaver does not exist.
Authentication via PAM is unlikely to work.

(xfce4-notifyd:1972): xfce4-notifyd-WARNING **: 19:54:55.803: Failed to truncate DB: column index out of range

** (process:16456): WARNING **: 19:55:23.005: /etc/pam.d/xfce4-screensaver does not exist.
Authentication via PAM is unlikely to work.

** (process:16627): WARNING **: 19:57:15.817: /etc/pam.d/xfce4-screensaver does not exist.
Authentication via PAM is unlikely to work.