message compose interruption hangs subsequent compose attempts

[svevang]

When creating a message, if a user quits the app leaving the message compose state in-process, then subsequently if that user opens the message compose.

A couple solutions here:

1. we could clean up the state each time the message compose dialog is opened
2. remove the message compose feature from the redux state flow

Not knowing what I was doing, I implemented the compose feature as part of a redux flow, e.g. when you hit a button in the compose flow, that keypress is recorded as part of the app state. This is overkill for a lot of reasons, but mainly because the user typically doesn't care about a half completed compositions. Though for example github has a nice feature where PR and comments are saved across page loads.