WebSockets: don't set outgoingAborted if outgoing is closed

If the WebSocket is already closed for writes, there's no need to set
outgoingAborted because there can be no more outgoing traffic.

This was showing up on protocol errors: the script would get an error
event describing what their WebSocket client said wrong (good), and
then a second error event complaining about a disconnect (bad).

src/workerd/api/web-socket.c++

@@ -450,8 +450,10 @@ kj::Promise<void> WebSocket::Accepted::createAbortTask(Native& native, IoContext
       LOG_EXCEPTION("webSocketWhenAborted", e);
     }
   }).then([this, &native]() {
-    // Other end disconnected prematurely. We may be able to clean up our state.
-    native.outgoingAborted = true;
+    if (!native.closedOutgoing) {
+      // Other end disconnected prematurely. We may be able to clean up our state.
+      native.outgoingAborted = true;
+    }
     if (!native.isPumping && native.closedIncoming) {
       // We can safely destroy the underlying WebSocket as it is no longer in use.
       // HACK: Replacing the state will delete `whenAbortedTask`, which is the task that is

src/workerd/server/server-test.c++

@@ -651,6 +651,8 @@ KJ_TEST("Server: test WebSocket errors: bad RSV bits") {
           `    server.addEventListener('message', (event) => {
           `      if (event.data === "getErrors") {
           `        server.send(JSON.stringify(errors))
+          `      } else if (event.data === "getErrorCount") {
+          `        server.send(errors.length.toString())
           `      } else {
           `        server.send(event.data);  // echo
           `      }
@@ -676,6 +678,8 @@ KJ_TEST("Server: test WebSocket errors: bad RSV bits") {
 
   auto errWsConn = test.connect("test-addr");
   errWsConn.upgradeToWebSocket();
+  errWsConn.send("\x81\x0dgetErrorCount");
+  errWsConn.recvWebSocketRegex("1");
   errWsConn.send("\x81\x09getErrors");
   errWsConn.recvWebSocketRegex(".*RSV bits.*");
 }