router: always respect message boundaries

The current implementaion of router socket does not
handle the full pipe and unroutable messages properly.
Namely, in those cases, the socket could route some
message parts into a wrong connection.

src/router.cpp

@@ -154,11 +154,9 @@ int zmq::router_t::xsend (msg_t *msg_, int flags_)
                 current_out = it->second.pipe;
                 if (!current_out->check_write ()) {
                     it->second.active = false;
-                    more_out = false;
                     current_out = NULL;
                 }
             } else if(fail_unroutable) {
-                more_out = false;
                 errno = EHOSTUNREACH;
                 retval = -1;
             }