Avoid calling SynchronousLoadData CompletionHandler more than once

https://bugs.webkit.org/show_bug.cgi?id=270030
rdar://109257007

Reviewed by Chris Dumez.

In some situations, a NetworkResourceLoader may call its SynchronousLoadData's
delayedReply CompletionHandler more than once. This change returns early if we
hit that case. I'm leaving the debug assertion so we investigate if this starts
happening frequently.

* Source/WebKit/NetworkProcess/NetworkResourceLoader.cpp:
(WebKit::sendReplyToSynchronousRequest):

Canonical link: https://commits.webkit.org/275465@main

Source/WebKit/NetworkProcess/NetworkResourceLoader.cpp

@@ -117,6 +117,9 @@ static void sendReplyToSynchronousRequest(NetworkResourceLoader::SynchronousLoad
     ASSERT(data.delayedReply);
     ASSERT(!data.response.isNull() || !data.error.isNull());
 
+    if (!data.delayedReply)
+        return;
+
     Vector<uint8_t> responseBuffer;
     if (buffer && buffer->size())
         responseBuffer.append(buffer->makeContiguous()->data(), buffer->size());