c94c2a47a3
If this slice ends up empty after parsing the HTTP response body, it means the body is not well-formed. We've probably encountered an error message produced by something that uses a different JSON schema, or an error that just happens to validate as JSON. An empty errcode.Errors slice is not a very useful thing to return, since its Error() output is just `<nil>`. Detect this case, and instend return an UnexpectedHTTPResponseError. Signed-off-by: Aaron Lehmann <aaron.lehmann@docker.com>