Add a check for 7z in unzip_file()
Add a check for 7z in unzip_file()

This should give a meaningful error message when zip7_path is misconfigured
cfossace/crits,lakiw/cripts,kaoscoach/crits,cfossace/crits,lakiw/cripts,dreardon/crits,korrosivesec/crits,ckane/crits,lakiw/cripts,ckane/crits,ckane/crits,dreardon/crits,jhuapl-marti/marti,cfossace/crits,jhuapl-marti/marti,ckane/crits,jhuapl-marti/marti,dreardon/crits,korrosivesec/crits,Lambdanaut/crits,Magicked/crits,dreardon/crits,Magicked/crits,kaoscoach/crits,Lambdanaut/crits,kaoscoach/crits,Magicked/crits,lakiw/cripts,korrosivesec/crits,cfossace/crits,kaoscoach/crits,korrosivesec/crits,Magicked/crits,jhuapl-marti/marti,Lambdanaut/crits,Lambdanaut/crits