fix(storage): check for nil drivers before creating blob transfer service

mentioned in commit 2f71e0b3

mentioned in merge request gitlab-org/build/CNG!922 (merged)

mentioned in merge request gitlab-com/gl-infra/k8s-workloads/gitlab-com!1569 (merged)

mentioned in merge request gitlab-com/gl-infra/k8s-workloads/gitlab-com!1602 (merged)

mentioned in merge request omnibus-gitlab!6064 (merged)

mentioned in merge request gitlab-development-kit!2503 (merged)