The worker task for an object descriptor may terminate because the underlying connection had an unrecoverable error.

In this case, we send an error to all active ranged reads (which could be "none"). Future ranged reads get a more obscure error. We should preserve the original I/O error so we can deliver it to future reads.

That is, calling ObjectDescriptor::read_range() when the worker is terminated should return the error that terminated the worker.