Fix scanByRawFilter containing - Select: 'COUNT'

[bsimpson53]

Trying to do a Select: 'COUNT' on a raw filter scan like:

var Dog = dynamoose.model('Dog');
var filter = {
  FilterExpression: 'details.timeWakeUp = :wakeUp',
  ExpressionAttributeValues: {
    ':wakeUp': '8am'
  },
  Select: 'COUNT'
};
Dog.scan(filter, { useRawAwsFilter: true }).exec()

generates this error:

Uncaught TypeError: Cannot read property 'map' of undefined
      at Response.<anonymous> (node_modules/dynamoose/lib/Scan.js:82:45)

Intercept the case where a raw filter scan where data is defined but data.Items is unpopulated and therefore by elimination the filter must have contained Select: 'COUNT'

[fishcharlie]

LGTM

[fishcharlie]

Thanks so much for this @bsimpson53, we will for sure try to get this in for version 0.9! Thanks again!!