[BFCache][WebSocket] don't dispatch error if websocket is closed in pagehide

https://bugs.webkit.org/show_bug.cgi?id=303619

Reviewed by Alexey Proskuryakov.

When the WebSocket is suspending and it was closed, or it is in the
middle of closing, it does not need to be closed separately (and dispatch
the error event).

There is already WPT test for that case. Now the test passes.

* LayoutTests/imported/w3c/web-platform-tests/websockets/back-forward-cache-with-open-websocket-connection-and-close-it-in-pagehide.window-expected.txt:
* Source/WebCore/Modules/websockets/WebSocket.cpp:
(WebCore::WebSocket::suspend):

Canonical link: https://commits.webkit.org/304082@main

Author: pgorszkowski-igalia

Source/WebCore/Modules/websockets/WebSocket.cpp

@@ -503,7 +503,7 @@ void WebSocket::contextDestroyed()
 
 void WebSocket::suspend(ReasonForSuspension reason)
 {
-    if (!m_channel)
+    if (!m_channel || m_state == CLOSING || m_state == CLOSED)
         return;
 
     if (reason == ReasonForSuspension::BackForwardCache) {