Task "Repair - Rebuild npm metadata" fails to rebuild npm package metadata

Issue

Customer has situation where there are multiple version of a npm package, but the npm root package metadata, only contains some of the versions. The missing versions can be downloaded if package tgz is directly requested.

Running task "Repair - Rebuild npm metadata" fails to rebuild npm metadata and does not add missing versions.

Steps to reproduce

1) Upload one npm packages, check metadata, has one versions, save this JSON output to a file
2) Upload another version, check metadata, has two versions.
3) Go to the file blobstore and find the bytes file for this metadata, and replace with step 1's JSON output (so now you have two tgz files but metadata contains one version).
4) Run task "Repair - Rebuild npm metadata" - no change to package metadata (still one version showing).
5) From UI delete package metadata.
6) Run task "Repair - Rebuild npm metadata" - package metadata is not rebuilt and you get a 404 response.

Expected behaviour

Running the task "Repair - Rebuild npm metadata", should rebuild the npm package metadata from all available versions (tgz) that are present for that package.