Fix writing of compressed cells containing structs with fields but empty data
Fix writing of compressed cells containing structs with fields but empty data

Fix the check for a structure with no fields

tbeu/matio,MaartenBent/matio,MaartenBent/matio,MaartenBent/matio,NJannasch/matio,tbeu/matio,tbeu/matio,NJannasch/matio,tbeu/matio,MaartenBent/matio