Assets do not seem to support locales correctly

[lc-jordanfelix]

The assets that we are using have multiple locales, and whenever we try to func (service *AssetsService) Get OR func (service *AssetsService) List we get a a panic: interface conversion: interface {} is nil, not string.

We believe this is due to the types as defined below:

// FileFields model
type FileFields struct {
	Title       string `json:"title,omitempty"`
	Description string `json:"description,omitempty"`
	File        *File  `json:"file,omitempty"`
}

// Asset model
type Asset struct {
	locale string
	Sys    *Sys        `json:"sys"`
	Fields *FileFields `json:"fields"`
}

whereas an example of the the json return from the get request is as follows:

{
  "sys": {...},
  "fields": {
    "title": {
      "en-GB": "..."
    },
    "description": {
      "en-GB": "..."
    },
    "file": {
      "en-GB": {...}
    }
  }
}

which would mean the assets would unmarshall into structs more like the below:

// FileFields model
type FileFields struct {
	Title       map[string]string `json:"title,omitempty"`
	Description map[string]string `json:"description,omitempty"`
	File        map[string]*File  `json:"file,omitempty"`
}

or similar.

We tried switching to single locale, and it still seems to have the same issue.