Comment 3 for bug 1489295

My idea was quite similar:
checking whether the highpriority Message was set / send and supressing the line identified by you.
From a quick look ps.production_result should be the correct method.

so this would result in something like

if (!ps.production_result == descr().out_of_resource_heading()) {
    ps.set_production_result(result_string);
}

However I am not sure whether this will be enough cause some other code in the mines could trigger either ps.set_production_result() or ps.unnotify_player