If no new commands are received, halt

Currently, we only exit the main loop when no new command is received
anymore (already taking any configured receive timeout into account).

However, if we don't receive a new command anymore, that should always
be considerd an unintentional interruption of the control flow. In that
case, we should stop program execution, as interrupting the
communication was an unexpected error event.

If interrupting the communication in order to continue with the rest of
the program was intentional, users will send a stop command. This will
end the main control loop at another code branch leading to a clean
shutdown of the external_control part in order to be able to continue
with the rest of the program.

Author: urfeex

resources/external_control.urscript

@@ -1003,7 +1003,8 @@ while control_mode > MODE_STOPPED:
     end
   else:
     textmsg("Socket timed out waiting for command on reverse_socket. The script will exit now.")
-    control_mode = MODE_STOPPED
+    stopj(STOPJ_ACCELERATION)
+    halt
   end
   exit_critical
 end