[$80] drone map errors unless drone has location data

[kbowerma]

In the process of adding a new drone we get an empty location property.

{
    "_id": {
        "$oid": "58629f8a01a1100004e8d83d"
    },
    "createdAt": {
        "$date": "2016-12-27T17:06:18.998Z"
    },
    "updatedAt": {
        "$date": "2016-12-27T17:06:18.998Z"
    },
    "serialNumber": "xx445533sss",
    "name": "regal-air",
    "type": "type1",
    "minSpeed": 2,
    "maxSpeed": 3,
    "maxFlightTime": 100,
    "maxCargoWeight": 10,
    "maxAltitude": 10,
    "cameraResolution": 1080,
    "videoResolution": 720,
    "hasWiFi": true,
    "hasBluetooth": true,
    "engineType": "engine",
    "numberOfRotors": 4,
    "hasAccelerometer": true,
    "hasGyroscope": true,
    "hasRadar": true,
    "hasGPS": true,
    "hasObstacleSensors": true,
    "hasUltraSonicAltimeter": true,
    "imageUrl": "htt://google.com",
    "status": "idle-ready",
    "specificationContent": "http://www.google.com/",
    "specificationImageUrl": "http://www.google.com/",
    "specificationPDFUrl": "http://www.google.com/",
    "provider": {
        "$oid": "584ad80eaebc030004a68a89"
    },
    "mileage": 30,
    "pilots": [],
    "currentLocation": [],
    
    "__v": 0
}

this will cause the map to throw erros and not display properly. We should pre-filter these where location is not empty