Glob pattern dist/**/* doesn't discover top level (within dist/) files

When using `buildkite-agent artifact download "dist/**/*" .` to download all artifacts in a compiled `dist` folder that has successfully been uploaded using `artifact_paths: "dist/**/*"` in the `pipeline.yml` file, the files downloaded do not contain files such as `dist/express.js` or `dist/worker.js`.

This seems [unexpected for the given glob pattern](https://www.digitalocean.com/community/tools/glob?comments=true&glob=dist%2F%2A%2A%2F%2A&matches=false&tests=%2F%2F%20This%20will%20match%20as%20it%20ends%20with%20%27.js%27&tests=dist%2Ffolder%2Ffile.js&tests=%2F%2F%20This%20won%27t%20match%21&tests=dist%2Ffile.js).

**NOTE**: The above pattern does download all files that are contained in subdirectories, for example, dist/apps/express.js and dist/apps/worker.js are successfully downloaded with the above command.

I have found a workaround by using `buildkite-agent artifact download "dist/**" .`, however, unsure if this was intended behaviour or not.

Start by reproducing the artifact upload from pipeline.yml with artifact_paths: "dist/**/*", then run buildkite-agent artifact download "dist/**/*" . against files at the top level and in subdirectories. Compare the result with the "dist/**" workaround and determine whether the documented glob behavior or the agent behavior should change; done means the intended behavior and workaround are clearly documented or the bug is fixed.

Written by the indexing model from the issue text.