Passthrough fingerprinted paths

[krallin]

If a path is already fingerprinted (e.g. because the {{asset-map}}
helper was used with a string that got replaced at build time), we can
return the fingerprinted file (i.e. the input we just got), rather than
undefined.

Note: this doesn't however require that the fingerprinted path be
correct: if it's not in the asset map, it won't be included.

[RuslanZavacky]

I'd suggest making it a reduce:

const map = get(this, 'map');

return Object.keys(map).reduce((acc, key) => {
  const value = map[k];
  return { [k]: value, value };
}, {});

[RuslanZavacky]

Thank you! Will try to merge most PRs and will test it out.