Node map generation seems to miss anonymous graph name

[gkellogg]

As noted in #143, the following inputs should create named graphs, but don't:

{
  "@context": {
    "@version": 1.1,
    "@vocab": "http://example.org/",
    "input": {"@container": "@graph"}
  },
  "input": [{
    "@id": "ex:someIdentifier",
    "@graph": [
      {"value": "x"},
      {"value": "y"}
    ]
  }]
}

and

{
  "@context": {
    "@version": 1.1,
    "@vocab": "http://example.org/",
    "input": {"@container": "@graph"}
  },
  "input": [{
    "@graph": [
      {"value": "x"},
      {"value": "y"}
    ]
  }]
}

[dlongley]

I think this is perhaps just a symptom of the special case code we've been discussing in #143 as removing it addresses the problem.