Work around another GMail IMAP bug (returns a NIL envelope for embedded messages)
Work around another GMail IMAP bug (returns a NIL envelope for embedded messages)

Fixes issue #59

dsbenghe/MailKit,eino-makitalo/MailKit,nachocove/MailKit,rajeshwarn/MailKit,jamie-dainton/MailKit,jstedfast/MailKit,FubarDevelopment/MailKit,sstraus/MailKit,mganss/MailKit,matt2003/MailKit