Fix switching to template mode

When we switch to template mode RichTextButton, which is dependent
on mailpoetData fails to render. The panel is hidden but it is hidden
in a subsequent render so we need to add check if mailpoet data are available.
[MAILPOET-6354]

packages/js/email-editor/src/components/personalization-tags/rich-text-with-button.tsx

@@ -76,6 +76,10 @@ export function RichTextWithButton( {
 		</>
 	);
 
+	if ( ! mailpoetEmailData ) {
+		return null;
+	}
+
 	return (
 		<BaseControl
 			id={ `mailpoet-settings-panel__${ attributeName }` }