#94 Creating a window should always fill an empty dock

[Ben Olden-Cooligan]

Context: When you save and restore certain layouts, there can be an empty dock area. For example:
1. "Open base as tree"
2. Right click on the tree tab and choose "Move to top"
3. Options/Windows/Save layout/1
4. Options/Windows/Restore layout/1

Given the above, then if you:
5. Restart scid
6. Open a new tree window (or any window)
The window opens a new tab in the bottom dock, not in the empty space.

I believe that opening a window should always prioritize filling the first empty space available, if any.

[Fulvio]

Thanks.
Fixed with:
https://sourceforge.net/p/scid/code/ci/9fa4ac1d0e513a574d1f9060eb2a54705b894a67/