TorBirdy crashes if tor process not running in Windows 8

(report of a friend's issue - most recent Thunderbird and TorBirdy on Windows 8)

So in Windows 8, if one starts Thunderbird when the tor process is not already running, it will crash.

Possible solutions:

• add a note in the top line of the extension description stating that TorBirdy requires tor browser to be running before starting Thunderbird. (This is in the documentation, but was overlooked in this case).
• fail gracefully with a popup that says that messages will not be sent over the Tor network until starting the tor process and restarting thunderbird.