Remove partially constructed accounts on resume

Resuming account setup activity when the account has been partially
constructed (the setup has not been finished) resulted in having unsaved
account with ID = -1 in the accounts list. The application would then on
resume proceed to messages list but there won't be any folders as the
setup has been aborted.

The fix clears the list of accounts on resume and create so that the
application properly reacts to the event of no setup accounts.

Fixes #3717.