Don't try sending on sharing channels.

The final main loop in do_ssh2_authconn will sometimes loop over all
currently open channels calling ssh2_try_send_and_unthrottle. If the
channel is a sharing one, however, that will reference fields of the
channel structure like 'remwindow', which were never initialised in
the first place (thanks, valgrind). Fix by excluding CHAN_SHARING
channels from that loop.

(cherry picked from commit 7366fde1d4)

ssh.c

@@ -10325,6 +10325,7 @@ static void do_ssh2_authconn(Ssh ssh, unsigned char *in, int inlen,
 	     * Try to send data on all channels if we can.
 	     */
 	    for (i = 0; NULL != (c = index234(ssh->channels, i)); i++)
+                if (c->type != CHAN_SHARING)
                     ssh2_try_send_and_unthrottle(ssh, c);
 	}
     }