force template redraw after adding a new button

Viewer/src/templating/templateManager.ts

@@ -379,6 +379,10 @@ export class Template {
         }
     }
 
+    public redraw() {
+        this.updateParams({});
+    }
+
     /**
      * Get the template'S configuration
      */

Viewer/src/viewer/defaultViewer.ts

@@ -57,8 +57,9 @@ export class DefaultViewer extends AbstractViewer {
         }
         if (plugin.addHTMLTemplate) {
             template.onHTMLRendered.add((tmpl) => {
-                plugin.addHTMLTemplate && plugin.addHTMLTemplate(tmpl);
+                plugin.addHTMLTemplate!(tmpl);
             });
+            template.redraw();
         }
 
         if (plugin.eventsToAttach) {