Inconsistent behavior when comparing a counted value with a negative value

Please include configurations and logs if available.

For confirmed bugs, please report:

- Version: 0.6.3
- Storage Backend: inmemory
- Mixed Index Backend: Lucene
- Link to discussed bug:
- Expected Behavior:
- Current Behavior:

When I compare a counted number with a negative value that is less than -2, an exception (e.g., `Not a legal range: [0, -2]`) is thrown. However, a negative value -1 or -2 cannot trigger this exception.

```
gremlin> :> g.V().where(__.inE('knows').count().is(not(lte(-3))))
Not a legal range: [0, -2]

gremlin> :> g.V().where(__.inE('knows').count().is(not(lte(-2))))
==>v[4216]
==>v[8312]
==>v[4312]
```

### Steps to Reproduce

```
Vertex bob = g.addV("person").property("name", "Bob").next();
Vertex alice = g.addV("person").property("name", "Alice").next();
Vertex book = g.addV("book").property("name", "book1").next();
Edge edge1 = g.addE("knows").from(bob).to(alice).next();
Edge edge2 = g.addE("write").from(alice).to(book).next();
g.E(edge2).property("duration", new Float(0.94461)).iterate();
```

Start by running the supplied Gremlin traversals against JanusGraph 0.6.3 with the in-memory storage backend and Lucene mixed index. Trace the count comparison and negative lte values to identify where the range exception is produced. Done means the behavior for negative values is consistent and the reproduction no longer produces an unexpected exception.

Written by the indexing model from the issue text.