change exception to warning when running hal2maf with default params on empty genome or seuqnce
change exception to warning when running hal2maf with default params on empty genome or seuqnce

glennhickey/hal,glennhickey/hal,glennhickey/hal,glennhickey/hal,glennhickey/hal,glennhickey/hal,glennhickey/hal,glennhickey/hal