agnosticbin: Check if queue is not NULL before doing other operations
agnosticbin: Check if queue is not NULL before doing other operations

This way it is easier to unref it correctly

Change-Id: I544900916defa91178343c1abf63e85503f9d316

TribeMedia/kms-elements,Kurento/kms-elements,shelsonjava/kms-elements,TribeMedia/kms-elements,Kurento/kms-elements,Kurento/kms-elements,shelsonjava/kms-elements,TribeMedia/kms-elements,shelsonjava/kms-elements