Merge pull request #507 from danlister/7.2.0-U4-5602

U4-5602 Dropdown List data type now shows an empty option after a page is saved

src/Umbraco.Web.UI.Client/src/views/propertyeditors/dropdown/dropdown.html

@@ -4,7 +4,8 @@
             class="umb-editor umb-dropdown"
             ng-switch-default
             ng-model="model.value"
-            ng-options="item.id as item.value for item in model.config.items">        
+            ng-options="item.id as item.value for item in model.config.items">
+        <option></option>
     </select>
     
     <!--NOTE: This ng-switch is required because ng-multiple doesn't actually support dynamic bindings with multi-select lists -->