refactor(EnvelopeLocked): add if smsExpiration-statetment to timer script

EnvelopeGenerator.Web/Views/Envelope/EnvelopeLocked.cshtml

@@ -96,6 +96,8 @@
         </details>
     </section>
 </div>
+@if (smsExpiration is not null)
+{
 <script nonce="@nonce">
     var expiration = new Date(@Html.Raw(JsonConvert.SerializeObject(smsExpiration)));
 
@@ -121,4 +123,5 @@
         var remainingTime = `${formattedMinutes}:${formattedSeconds}`;
         element.textContent = remainingTime;
     }, 1000);
-</script>
+</script>    
+}