prevent duplicate key error if same layer added several time to the same basemap

src/components/Map/LayerSelector.vue

@@ -29,7 +29,7 @@
     >
       <div
         v-for="layer in basemap.layers"
-        :key="basemap.id + '-' + layer.id"
+        :key="basemap.id + '-' + layer.id + Math.random()"
         class="layer-item transition visible item list-group-item"
         :data-id="layer.id"
       >