Error with fullscreen terminal in NeoVim

For some reason whenever I use a fullscreen window in NeoVim (specifically using the "FZF" vim plugin), and hit "enter" to select a result I get the following errors:

```
Error detected while processing function 449:
line 10:
E444: Cannot close last window
Press ENTER or type command to continue
Error detected while processing function 449:
line 12:
E474: Invalid argument: tabnext 2
Press ENTER or type command to continue
Error detected while processing function 449:
line 13:
E16: Invalid range: 3wincmd w
Press ENTER or type command to continue
```

Start by reproducing the fullscreen NeoVim workflow with the FZF plugin and pressing Enter to select a result. Trace the reported E444, E474, and E16 errors to determine why the selection leaves invalid windows or tabs; done means selecting a result works without any of these errors.

Written by the indexing model from the issue text.