Pass the SecureMimeContext.CertificateStore's certificates to the EnvelopedCms.Decrypt()
Pass the SecureMimeContext.CertificateStore's certificates to the EnvelopedCms.Decrypt()

If we don't do this, EnvelopedCms.Decrypt() might not be able to find
the private key in order to actually decrypt the data because it will
only look in the system certificate stores.

jstedfast/MimeKit,nachocove/MimeKit,nachocove/MimeKit,jstedfast/MimeKit,nachocove/MimeKit,jstedfast/MimeKit