Preview window does not update when switching tabs

[TrentonZero]

Given: Select an event in "follow" tab
Given: Switch to "all" tab
Given: Select an event in "all" tab
When: Switching to "follow" tab
Expect: Preview window will show the currently highlighted message in "follow"
Actual: Preview window shows the currently highlighted message from "all"

(Alternatively, since there is only one preview window, allow only one message to be selected at a time across all tabs.)

Normally, it's pretty easy to know what is going on, but I got distracted a few times and when I looked back to the app, was surprised to see very suspicious BTC advertisements from Uncle Bob.

[unclebob]

Giggle. Yeah, I've got this on in my list to fix.