We need to apply the wallpaper anchors after the lockscreen theme is loaded, otherwise they won't be set properly and we end up with a black background.

This issue was triggered by !84

The reason why this wasn't noticed on Plasma Desktop, was that its lockscreen theme draws a FastBlur above the wallpaper in the background which will still correctly display the wallpaper item.

I had forgotten about that I used that as a workaround in Plasma Mobile for months... oops