We should be able to query cardinality

[klahnakoski]

...even if it is null

{
    "from": "meta.columns",
    "select": "cardinality",
    "where": {
        "and": [
            {
                "eq": {
                    "table": "fx-test"
                }
            },
            {
                "eq": {
                    "name": "result.ok"
                }
            }
        ]
    }
}

[klahnakoski]

added test https://github.com/mozilla/ActiveData/pull/103/commits/fc857e7a74f94991f080cee4a2c0a61fbce77a56#diff-139eb3bb045bdea04c4eb4287087e781R187

[klahnakoski]

bad test, still broken