peekSockAddr: Non-exhaustive patterns in case

[dylex]

When doing a recvFrom on (in this case) a unix socket where the remote side is not connected, and more generally whenever the peer is not identified, the returned sackaddr will be AF_UNSPEC, resulting in the error:

Network/Socket/Internal.hsc:(298,2)-(314,60): Non-exhaustive patterns in case

Perhaps this is just not supported and one must use recv (which works), but then a nicer (IO) error would be preferable. Ideally, it would return a Maybe SockAddr?.