Fix for FileUploadParser with version 3.x

[askholme]

Output from parsers ends up in a Django MergeDict and they exists elements to be dicts - not None

Right now if FileUploadParser is used then trying to access request.data['file'] will give ** TypeError: 'NoneType' object has no attribute 'getitem'

Making sure that the data part is an empty dict fixes this

[lovelydinosaur]

Looks reasonable, but I'm uncertain why we havn't seen any issues raised before if this is currently broken - is it newly broken in 3.x? If not it'd be super surprising as FileUploadParser has been part of the library for quite a while now.

[askholme]

Can't tell as i just started using the framework.

Do note that i'm using the parser for a custom method on a viewset access request.data directly as per below. This gives an error because request.data is a mergedict where __getitem__ loops over the underlying dicts and then tries to use __getitem__ on the None returned from FileUploadParser.

Maybe the serializers use another method for access FileUploadParser data?

@list_route(methods=['put'],permission_classes=[permissions.IsAuthenticated],parser_classes=   [FileUploadParser])
    def raw(self,request):
        img = Image(image=request.data['file'],user=self.request.user)
        img.save()
        return Response(ImageSerializer(img).data)