Use fetch() in a way that works for file URLs

[hughns]

fetch returns a response code of 0 when it successfully loads a file:// resource.

This means we can't just rely on response.ok.

Required for #2994

[toger5]

I think the condition

 !response.ok &&
        (!response.url || !response.url.startsWith("file:"))

Is un-intuitive enough so that is makes sense to move it into

/**
* Dedicated explanation why we need this for the file case here.
*/
isErrorNetworkOrFileResponse(response){
return  !response.ok &&
        (!response.url || !response.url.startsWith("file:"));
}

isErrorNetworkOrFileResponse can probably get a better name

[toger5]

Are you sure res.status === 404 || res.status === 0 implies response.ok === false (just double checking to make sure the or condition was actually unnecassary.)

[toger5]

why is it an && condition if we cannot trust the response status?
It (response.ok) is still guaranteed to be false in a failure case but it is also false if it is a success?

[hughns]

response.ok is defined as:

The ok read-only property of the Response interface contains a Boolean stating whether the response was successful (status in the range 200-299) or not.

fetch returns a status of 0 for file:// URLs.

I will put this into a function and clarify with comments.

[toger5]

Thanks with this change i now fully get what is happening.