prevent customForm being added twice at edit

src/views/feature_type/Feature_type_edit.vue

@@ -340,11 +340,19 @@ export default {
     },
 
     addCustomForm(customForm) {
+      if (
+        customForm &&
+        this.customForms.some((cf) => cf.name === customForm.name)
+      ) {
+        //* abort if customForm already exists (because watcher can update again)
+        return;
+      }
       this.dataKey += 1; // * increment counter for key in v-for
       let newCustomForm = {
         dataKey: this.dataKey,
       };
       if (customForm) {
+        //* if adding an existing customForm -> add its property to newCustomForm containing only dataKey
         newCustomForm = { ...newCustomForm, ...customForm };
       }
       this.$store.commit("feature_type/ADD_CUSTOM_FORM", newCustomForm); // * create an object with the counter in store