Fixed
* Users with attachments open in tabs saw an error on Thunderbird restart
* Sending from unified or local folder failed if no default account was set
* Delete button could remove attachment instead of message
* Message list scrolled back when returning to mail tab after opening a message
OBS-URL: https://build.opensuse.org/package/show/mozilla:Factory/MozillaThunderbird?expand=0&rev=833
