Fix: only fire event when instance is available (issue 17847) (#17987)

* only fire event when instance is available

* avoid js issue when no markup

src/Umbraco.Web.UI.Client/src/views/propertyeditors/rte/rte.component.js

@@ -256,7 +256,7 @@
                         toolbar: editorConfig.toolbar,
                         model: vm.model,
                         getValue: function () {
-                          return vm.model.value.markup;
+                          return vm.model.value.markup ?? "";
                         },
                         setValue: function (newVal) {
                           vm.model.value.markup = newVal;
@@ -348,7 +348,9 @@
           // But I'm not sure it's needed, as this does not trigger the RTE
           if(modelObject) {
             modelObject.update(vm.model.value.blocks, $scope);
-            vm.tinyMceEditor.fire('updateBlocks');
+            if (vm.tinyMceEditor) {
+              vm.tinyMceEditor.fire('updateBlocks');
+            }
             onLoaded();
           }
       }