Automatically hidden taskbar doesn't show up over maximized MetroWindow

Nobody has claimed this yet.

## Describe the bug

When the taskbar is set to hide automatically, it doesn't show up over a maximized MetroWindow. Also, still when it's maximized , there's a little gap at the bottom (or wherever the taskbar is positionned) of the MetroWindow that displays the program behind (or the Wallpaper if there's nothing behind). If you click on that gap it obviously focuses the program that was behind.

## Steps to reproduce

1. Set your taskbar to hide automatically (Right click on taskbar => taskbar settings => Automatically hide taskbar in desktop mode).
2. Run the sample application in [MahApps bug demo.zip](https://github.com/MahApps/MahApps.Metro/files/6150962/MahApps.bug.demo.zip) (Unfortunately I can't post a full github repository).

3. Maximize the MetroWindow if it isn't maximized already.
4. Move the cursor to where your taskbar is.
5. Taskbar doesn't show up. (And you can see the little gap I was talking about).
6. Click on the gap. The application behind gets focus.

## Expected behavior

The taskbar shows up when the cursor is over it. The little gap at the bottom (or wherever the taskbar is positionned) is filled with the MetroWindow's content.

## Environment

```
MahApps.Metro version: v2.4.3
Windows build number: Win10 1803 [Version 17134.2087]
Visual Studio: Professional 2019 16.6.4
Target Framework: .Net Framework 4.6.1
```

## Screenshots


Start by running the linked MahApps bug demo.zip on Windows with the taskbar set to auto-hide, then maximize the MetroWindow and reproduce the missing taskbar and bottom gap. Investigate the maximized-window behavior that affects taskbar interaction. Done means the taskbar appears when hovered and the MetroWindow fills the taskbar area without exposing or focusing the application behind it.

Written by the indexing model from the issue text.