shell: Remove last workspace if it follows empty active workspace

[ids1024]

Partly fixes pop-os/cosmic-workspaces-epoch#83, but it seems like there's at least one other issue with workspaces not being removed when they should be.

The if condition got a bit complicated here, so I've split it up and inverted the condition.

[ids1024]

Another issue here is pending_activations. retain_tokens removes tokens with a 5 second delay, so the token added with create_external_token() when it's not used make is_empty() on the workspace false until that delay is over.

Not sure the right change for that one.

[Drakulix]

Another issue here is pending_activations. retain_tokens removes tokens with a 5 second delay, so the token added with create_external_token() when it's not used make is_empty() on the workspace false until that delay is over.

Not sure the right change for that one.

The idea here is that windows should spawn on the workspace they were invoked on. So the right fix would probably be to re-run the cleanup logic once the 5 second delay runs out?