Fix issue when reloading while a reload is pending.

I noticed of an issue with the `MULTI_THREAD` feature, where an
application would receive a `CancellationError` in the very rare
(possible right now?) occurrence where we're reloading while a reload
operation is already pending.

We don't ever want to leak `CancellationError` which is just an internal
mechanism. I thought that we can just ignore that one.

src/core/main/worker/worker_main.ts

@@ -884,6 +884,10 @@ function loadOrReloadPreparedContent(
         );
       },
       (err: unknown) => {
+        if (TaskCanceller.isCancellationError(err)) {
+          log.info("WP: A reloading operation was cancelled");
+          return;
+        }
         sendMessage({
           type: WorkerMessageType.Error,
           contentId,