Bug 1637869 - P7. Call DisconnectChildListeners when an error occurs. r=mattwoodrow

This will allow the DocumentChannel to be removed from the loading group and the docshell to stop waiting for for the ParentProcessDocumentChannel to do something.

Depends on D77201

Differential Revision: https://phabricator.services.mozilla.com/D77202

netwerk/ipc/DocumentLoadListener.cpp

@@ -805,6 +805,7 @@ void DocumentLoadListener::FinishReplacementChannelSetup(nsresult aResult) {
     if (NS_FAILED(aResult)) {
       mChannel->Cancel(aResult);
       mChannel->Resume();
+      DisconnectChildListeners(aResult, aResult);
       return;
     }
     ApplyPendingFunctions(mChannel);