Ignore temporary recipient resolve errors

* src/cryptocontroller.cpp (CryptController::resolve_keys):
Add unlikely error handling if recipients could not be resolved here.
* src/mail.cpp (Mail::getRecipients_o): Ignore error when
getting recipients.

When editing the recipients of a draft Outlook still has an
recipient object for the former recipient but does not provide
properties on it. So the address resolution fails. We can
treat the mail as having no recipients and only have a
fatal error if we can't resolve recipients in the cryptcontroller.

• GnuPG-Bug-Id: T4129