Fixed ImapFolder.GetMessage(), GetBodyPart() and GetStream() to never return null
Fixed ImapFolder.GetMessage(), GetBodyPart() and GetStream() to never return null

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