Fix misunderstanding of netrigctl_transaction() return value

netrigctl_transaction()  returns  either  an  error  code  (-ve  int),
RIG_OK, or the number of characters read from the protocol stream. +ve
return  values indicate  successful  parsing of  stream  data, not  an
error.

dummy/netrigctl.c

@@ -191,7 +191,7 @@ static int netrigctl_open(RIG *rig)
     {
         if (buf[0]) { sscanf(buf, "CHKVFO %d", &priv->rigctld_vfo_mode); }
     }
-    else
+    else if (ret < 0)
     {
         rig_debug(RIG_DEBUG_WARN, "%s: chk_vfo error: %s\n", __FUNCTION__,
                   rigerror(ret));