When some (invalid) arches are filtered out, we can have empty list. Don't spawn such task. (e.g. with --arch noarch)
PR #973
Metadata Update from @tkopecek: - Issue set to the milestone: 1.17 - Issue tagged with: easyfix
Commit cfe859e1 fixes this issue
This issue has been migrated to Fedora Forge: https://forge.fedoraproject.org/koji/koji/issues/974
Please continue any further discussion there.