mod_report_forward: Fix traceback on error message passed to datetime function If archive:get() returns an error, e.g. because it can't find a message with the given ID, it may return e.g. nil, "item-not-found" or similar where the error condition ends up in reported_message_time, which gets passed to util.datetime, which thus ends up doing math to a string or error object.

local hostname = module:get_option_string("sasl_hostname", module.host);

module:hook("stream-features", function(event)
	local features = event.features;
	local mechs = features:get_child("mechanisms", "urn:ietf:params:xml:ns:xmpp-sasl");
	if mechs then
		mechs:tag("hostname", { xmlns = "urn:xmpp:domain-based-name:1" })
			:text(hostname):up();
	end
end);