fixed bug in CellLab wherein time in main loop could advance beyond specified run duration
fixed bug in CellLab wherein time in main loop could advance beyond specified run duration

amandersillinois/landlab,SiccarPoint/landlab,Carralex/landlab,ManuSchmi88/landlab,cmshobe/landlab,laijingtao/landlab,Carralex/landlab,ManuSchmi88/landlab,RondaStrauch/landlab,cmshobe/landlab,laijingtao/landlab,cmshobe/landlab,landlab/landlab,RondaStrauch/landlab,SiccarPoint/landlab,csherwood-usgs/landlab,csherwood-usgs/landlab,ManuSchmi88/landlab,amandersillinois/landlab,Carralex/landlab,landlab/landlab,landlab/landlab,RondaStrauch/landlab