fixed bug reading back bng output when some species are not present in any reaction
fixed bug reading back bng output when some species are not present in any reaction

spgarbet/pysb,pysb/pysb,d-fan/pysb,d-fan/pysb,neurord/pysb,spgarbet/pysb,johnbachman/pysb,spgarbet/pysb,jmuhlich/pysb,alubbock/pysb-legacy,neurord/pysb,johnbachman/pysb,alubbock/pysb-legacy,alubbock/pysb-legacy,alubbock/pysb-legacy,LoLab-VU/pysb,d-fan/pysb,alubbock/pysb,neurord/pysb,LoLab-VU/pysb