Closing a tab can cause circular history

[bobbylight]

Because we blindly go to the prior route when a compound tab is closed, this can cause circular closings:

1. Open compound A
2. Open compound B
3. Click to focus compound A
4. Close compound A
5. You should be on compound B now
6. Close compound B

Expected behavior:
You are booted to some prior tab, such as the Search tab

Actual behavior:
You are booted back to compound A, which is magically reopened in a tab.

Perhaps the simplest fix is to navigate to the Search tab if the prior tab is no longer open?