fix(storage): prevent panic in inmemory driver
Cherry-pick from upstream: https://github.com/distribution/distribution/pull/3815
Upstream Issue: https://github.com/distribution/distribution/issues/3614
Edited by Hayley Swimelar
Cherry-pick from upstream: https://github.com/distribution/distribution/pull/3815
Upstream Issue: https://github.com/distribution/distribution/issues/3614