Improve lake mapper error messages
Improve lake mapper error messages

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