Set cache buster equal to 0 when there is no affected tables in the mapconfig

lib/api/middlewares/last-updated-time-layergroup.js

@@ -11,6 +11,10 @@ module.exports = function setLastUpdatedTimeToLayergroup () {
             }
 
             if (!affectedTables) {
+                res.locals.cache_buster = 0;
+                layergroup.layergroupid = `${layergroup.layergroupid}:${res.locals.cache_buster}`;
+                layergroup.last_updated = new Date(res.locals.cache_buster).toISOString();
+
                 return next();
             }