Properly hide warning, when no expiration time has been set

Change-Id: I2d92eacb7515c84f902a7317e1a80c009ae07ebe

web/gr-serviceuser-tokens.ts

diff --git a/web/gr-serviceuser-tokens.ts b/web/gr-serviceuser-tokens.ts
index 06df8ea..2959eaa 100644
--- a/web/gr-serviceuser-tokens.ts
+++ b/web/gr-serviceuser-tokens.ts
@@ -145,6 +145,10 @@
         .lifeTimeInput {
           min-width: 23em;
         }
+        :host([hidden]),
+        [hidden] {
+          display: none !important;
+        }
 
         # Remove when material styles are available for plugins
         md-outlined-text-field {