Fixed bug when reindexing cells by xy.
Fixed bug when reindexing cells by xy.

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