Map / External map viewer should not redirect to map app

When an external mapviewer is configured, location URL is changed.
Only change location if buildAddToMapConfig return a config. If not, then it has redirected to the external viewer.

Backport attempt of
https://github.com/geonetwork/core-geonetwork/pull/6548/files ;
untested, will need help from @tkohr to validate.

web-ui/src/main/resources/catalog/views/default/module.js

@@ -413,9 +413,12 @@
         addMdLayerToMap: function (link, md) {
           // This is probably only a service
           // Open the add service layer tab
-          $location.path("map").search({
-            add: encodeURIComponent(angular.toJson([buildAddToMapConfig(link, md)]))
-          });
+          var config = buildAddToMapConfig(link, md);
+          if (angular.isObject(config)) {
+            $location.path('map').search({
+              add: encodeURIComponent(angular.toJson(
+                [config]))});
+          }
           return;
         },
         addAllMdLayersToMap: function (layers, md) {