return 0 when score or reviews is undefined

[ftcvlad]

For keyword scores overall difficulty and traffic score may be null. This happens if itunes returns apps with 'score' or 'reviews' fields undefined (for example, if an app doesn't have reviews). Hence, it affects overall difficulty and traffic score calculation.

Example result:

"difficulty": {
    "titleMatches": {
      "exact": 0,
      "broad": 0,
      "partial": 0,
      "none": 10,
      "score": 0
    },
    "competitors": {
      "count": 1,
      "score": 1.09
    },
    "installs": {
      "avg": null
      "score": null
    },
    "rating": {
      "avg": null
      "score": null
    },
    "age": {
      "avgDaysSinceUpdated": 557.1,
      "score": 1
    },
    "score": null
  }

[facundoolano]

Thanks!