saml2_Message: Decrypt the NameID element if it is encrypted.
saml2_Message: Decrypt the NameID element if it is encrypted.

Fixes issue 206

simplesamlphp/saml2,sitya/saml2,cb8/saml2,sgomez/saml2,madmatt/saml2,ArtemTeleshev/php-saml2,newmen/saml2