Fix support side anonymous authentication

[lbeuster]

I could not use the DBus-Server (Transport.SASL) for anonymous auth via tcp.

The server side authentication (Transport.SASL) had two problems:

• There was an if-statement rejecting the auth method if the command data was null - for anonymous auth the command data is always null. So I commented out this if-statement (the commented out code should be removed completely)
• If one auth method fails the server should not return an ERROR but instead use REJECT so that the client can use the next auth method (ERROR causes the client to stop immediately) (see SASL.do_response). Currently I only replaced one ERROR with REJECT but I think all ERRORS in this method should be replaced with REJECT, because the client can continue with auth in all these cases.

[lbeuster]

Did the merge and recreated my changes. Errors in the code were still there.