Response without any content (e.g. 204 No Content) returns the XHR object itself instead of empty response

[DCoderLT]

When handling an empty response, at reqwest.js#324, the entire if() that transforms resp from the XHR object to the parsed response content is skipped due to r being empty, and the completion callbacks afterwards use the old value of resp, the XHR object itself, as the response.

It seems quite surprising to receive a non-empty response in this case. This behaviour can be worked around using dataFilter, but it seems to me that the library should be handling this internally.