Moving the tab from the window to another doesn't close the window

[Adam Bieńkowski]

Moving the last tab from the window to another window causes it to show an empty space with a spinner.

Steps to reproduce:
1. Open one Files window with some tabs (doesn't matter how many)
2. Open another Files window with only one tab
3. Drag'n drop this tab from this window to the one opened previously
4. The window without any tabs shows a spinner and empty space

Expected behaviour:
The window without tabs closed or adds a new tab with the default user Home directory