The window position is not stored correctly if the Taskbar is not at bottom

[punker76]

Describe the bug

Issue came up at ChocolateyGui chocolatey/ChocolateyGUI#793

... the "WINDOWPLACEMENT" / "normalPosition" parameter in the "user.xml" file;

The stored x(left) / y(top) coords are (apparently) relative to the full Screen area, but when the GUI opens, it applies them relative to the Screen area without the Taskbar

So, if you have the Taskbar on the left or top of the screen, the GUI window opens not where it was, but with an according offset.

Steps to reproduce

Put the Taskbar on left/right/top.

Expected behavior

The position of the window should be restored correctly.

Actual behavior

The position of the window will be moved.

Environment

MahApps.Metro version: v2.4.4
Windows build number: Win10 1909 18363.1316
Target Framework: .Net Core 3.1 (v4.5.2, v4.7.2)