bug(storage): UploadOrResume completes when a chunk is cancelled or fails #473

Found this while working on #470.

When a chunk after the first one is cancelled or fails, UploadOrResume completes normally, but the file is only partly uploaded.

var cts = new CancellationTokenSource();
await storage.From("bucket").UploadOrResume(data, "a.bin", options, (_, _) => cts.Cancel(), cts.Token);
// completes after the first 6 MB chunk, the rest is never sent

A timeout or network error on a later chunk does the same. If it fails before the first chunk is sent (cancel, timeout, connection refused), it throws a NullReferenceException instead of the real error.

BirdMessenger's TusPatchWithChunkAsync catches every exception, passes it to OnFailedAsync and returns the last response it got. ResumableUploadAsync sets OnFailedAsync to a no-op and only checks that response, so it sees the previous chunk's 204, or null.