Fixed potential stalls in javascript.

TrafficLights/Pages/Index.cshtml

@@ -98,6 +98,7 @@
                     if (this.status !== 200)
                     {
                         console.log("Failed update: status " + this.status);
+                        isSending = false;
                         return;
                     }
                     let static_path_prefix = "/images/";
@@ -144,6 +145,7 @@
                         catch (err)
                         {
                             console.dir(err);
+                            isSending = false;
                         }
                     }
                     // Important note: Due to marginal overshoot of scheduled timing, it is possible for time-remaining to be very slightly negative