The on-release-upload-tarball-etc-to-release part of workflow is not idempotent, as it will fail 2nd time (e.g., manually triggered) after succeeding the first time, even though other parts of workflow would still be useful in some cases. Now it checks for presence of the tarball before uploading tarball (else does not do it); same with zip.

The on-release-upload-tarball-etc-to-release part of workflow is not idempotent, as it will fail 2nd time (e.g., manually triggered) after succeeding the first time, even though other parts of workflow would still be useful in some cases. Now it checks for presence of the tarball before uploading tarball (else does not do it); same with zip. #613