Bug 1765339 - Update error handling in PipeToPump r=evilpie

Differential Revision: https://phabricator.services.mozilla.com/D144035

dom/streams/ReadableStreamPipeTo.cpp

@@ -503,12 +503,16 @@ void PipeToPump::ShutdownWithActionAfterFinishedWrite(
   RefPtr<Promise> p = aAction(aCx, thisRefPtr, aError, rv);
 
   // Error while calling actions above, continue immediately with finalization.
-  rv.WouldReportJSException();
-  if (rv.Failed()) {
+  if (rv.MaybeSetPendingException(aCx)) {
+    JS::Rooted<Maybe<JS::Value>> someError(aCx);
+
     JS::Rooted<JS::Value> error(aCx);
-    bool ok = ToJSValue(aCx, std::move(rv), &error);
-    MOZ_RELEASE_ASSERT(ok, "must be ok");
-    JS::Rooted<mozilla::Maybe<JS::Value>> someError(aCx, Some(error.get()));
+    if (JS_GetPendingException(aCx, &error)) {
+      someError = Some(error.get());
+    }
+
+    JS_ClearPendingException(aCx);
+
     Finalize(aCx, someError);
     return;
   }