rm throw from getAvailableServiceWorker

* There are cases where getAvailableServiceWorker returning `null` is ok
and it safe to move on so the following was done.
   - Removed the throw
   - Added a warning log etnry
   - Added null handling where this method is being called.

src/helpers/page/ServiceWorkerUtilHelper.ts

@@ -13,11 +13,11 @@ export default class ServiceWorkerUtilHelper {
   }
 
   // A ServiceWorkerRegistration will have a ServiceWorker in 1 of 3 states, get which ever is available.
-  static getAvailableServiceWorker(registration: ServiceWorkerRegistration): ServiceWorker {
+  static getAvailableServiceWorker(registration: ServiceWorkerRegistration): ServiceWorker | null {
     const availableWorker = registration.active || registration.installing || registration.waiting;
-    // This should never throw unless ServiceWorkerRegistration is pointing to a worker that is completely gone.
+    // This never be null unless ServiceWorkerRegistration is pointing to a worker that is completely gone.
     if (!availableWorker) {
-      throw new Error("Could not find an available ServiceWorker instance!");
+      Log.warn("Could not find an available ServiceWorker instance!");
     }
     return availableWorker;
   }

src/libraries/WorkerMessenger.ts

@@ -152,8 +152,14 @@ export class WorkerMessenger {
       return;
     }
 
+    const availableWorker = ServiceWorkerUtilHelper.getAvailableServiceWorker(workerRegistration);
+    if (!availableWorker) {
+      Log.error("`[Worker Messenger] [Page -> SW] Could not get ServiceWorker to postMessage!");
+      return;
+    }
+
     // The postMessage payload will still arrive at the SW even if it isn't active yet.
-    ServiceWorkerUtilHelper.getAvailableServiceWorker(workerRegistration).postMessage({
+    availableWorker.postMessage({
       command: command,
       payload: payload
     });

src/managers/ServiceWorkerManager.ts

@@ -83,6 +83,10 @@ export class ServiceWorkerManager {
   // Get the file name of the active ServiceWorker
   private static activeSwFileName(workerRegistration: ServiceWorkerRegistration): string | null {
     const serviceWorker = ServiceWorkerUtilHelper.getAvailableServiceWorker(workerRegistration);
+    if (!serviceWorker) {
+      return null;
+    }
+
     const workerScriptPath = new URL(serviceWorker.scriptURL).pathname;
     const swFileName = new Path(workerScriptPath).getFileName();