fix(datastore): check for blob access before importing layer

mentioned in commit e9fb42a9

mentioned in issue #549 (closed)

mentioned in merge request gitlab-org/build/CNG!852 (merged)

mentioned in merge request gitlab-org/charts/gitlab!2334 (merged)

mentioned in merge request gitlab-com/gl-infra/k8s-workloads/gitlab-com!1435 (merged)

mentioned in merge request gitlab-com/gl-infra/k8s-workloads/gitlab-com!1436 (merged)

mentioned in merge request omnibus-gitlab!5827 (merged)

mentioned in merge request gitlab-development-kit!2385 (merged)