[SMTP] Fails to send message after a change for bug 737903
[SMTP] Fails to send message after a change for bug 737903

Some SASL authentications can return NULL challenge as a valid
value, without providing an error. This detail the previous change
missed, thus some authentication types failed for SMTP.

tintou/evolution-data-server,tintou/evolution-data-server,tintou/evolution-data-server,matzipan/evolution-data-server,matzipan/evolution-data-server,matzipan/evolution-data-server,tintou/evolution-data-server,matzipan/evolution-data-server,matzipan/evolution-data-server