Request with already cancelled CancelToken

[AndreiMisiukevich]

Does a server request still get initiated if an already-cancelled CancelToken is passed along with the request? cancelToken.isCancelled // true

I've briefly looked through the code and didn't find any places like that
if (cancelToken?.cancelError != null) throw cancelToken!.cancelError!;

And if my assumption is correct, a server request always gets initiated. And then immediately gets cut off.

[AlexV525]

Implemented in #2251.