don't crash if password not specified for sasl acquirecredentials
don't crash if password not specified for sasl acquirecredentials

Yottaa/mgo.v2,hexadecy/mgo,deafgoat/mgo,DroiTaipei/mgo,Yottaa/mgo.v2,deafgoat/mgo,DroiTaipei/mgo,DroiTaipei/mgo,hexadecy/mgo,DroiTaipei/mgo,hexadecy/mgo,deafgoat/mgo,hexadecy/mgo,deafgoat/mgo,Yottaa/mgo.v2,Yottaa/mgo.v2