404 is mapped to ResourceError::NotFound
401,402,403,407 are mapped to ResourceError::NotAuthorized
other error status codes are mapped to ResourceError::OpenRead
This mirrors the behavior in souphttpsrc
Otherwise there might still some thread waiting for the receiver to
consume a message and we would deadlock here. Dropping the receiver
drops all messages and unblocks them all immediately.
Also don't panic when sending messages to a dropped receiver.