exporter: unable to use IPLDResolver .get(path) for inexistent paths

[pgte]

While developing the subtree support feature, I tried using the IPLD resolver to solve paths inside CBOR / non-UnixFS nodes, and it hanged, never returning. This line should be something like:

dag.get(cid, path.rest, (err, node) => {
   // now we should have node.remainderPath to resolve further...

[daviddias]

ping @vmx

[vmx]

The code changed a lot since the bug was reported (I think it can be closed). This is a UnixFS issue, not an IPLD one, hence assigning to @achingbrain.