clean up some handle/client reference counting errors in error cases.

We weren't consistent about who should unreference the handle in
case of network error. Make it consistent so that it's always the
client code responsibility to unreference the handle - either
in the callback or right away if send function failed and the callback
will never be called.

lib/isc/netmgr/tcpdns.c

@@ -470,8 +470,7 @@ isc__nm_tcpdns_send(isc_nmhandle_t *handle, isc_region_t *region,
 	REQUIRE(sock->type == isc_nm_tcpdnssocket);
 
 	if (sock->outer == NULL) {
-		/* The socket is closed, just issue the callback */
-		cb(handle, ISC_R_FAILURE, cbarg);
+		/* The socket is closed */
 		return (ISC_R_NOTCONNECTED);
 	}