add '...@append' method to block properties

src/content/ContentBuilder.cpp

@@ -93,8 +93,8 @@ std::unique_ptr<Content> ContentBuilder::build() {
         def->rt.surfaceReplacement = content->blocks.require(def->surfaceReplacement).rt.id;
         if (def->properties == nullptr) {
             def->properties = dv::object();
+            def->properties["name"] = def->name;
         }
-        def->properties["name"] = def->name;
     }
 
     for (ItemDef* def : itemDefsIndices) {