Show error if tag name is empty

Signed-off-by: Gary Kim <gary@garykim.dev>

apps/systemtags/js/admin.js

@@ -1,5 +1,6 @@
 /**
  * @copyright Copyright (c) 2016 Joas Schilling <coding@schilljs.com>
+ * @copyright Copyright (c) 2019 Gary Kim <gary@garykim.dev>
  *
  * @license GNU AGPL version 3 or any later version
  *
@@ -83,6 +84,11 @@
 				userAssignable: level === 3
 			};
 
+			if (!data.name) {
+				OCP.Toast.error(t('systemtags_manager', 'Tag name is empty'));
+				return;
+			}
+
 			if (tagId) {
 				var model = this.collection.get(tagId);
 				model.save(data);