MediaSet: do not start wait if it is already terminated
MediaSet: do not start wait if it is already terminated

Change-Id: Ib31f3f8fabeb2869aab7540a9125b8136fe9c100

TribeMedia/kms-core,shelsonjava/kms-core,shelsonjava/kms-core,ESTOS/kms-core,shelsonjava/kms-core,Kurento/kms-core,Kurento/kms-core,Kurento/kms-core,ESTOS/kms-core,ESTOS/kms-core,Kurento/kms-core,TribeMedia/kms-core,shelsonjava/kms-core,ESTOS/kms-core,TribeMedia/kms-core,TribeMedia/kms-core