Bug 1607984 - P10. Wait until OnStopRequest has been called to clear mRequest. r=valentin

The code assumed that nsJARChannel::RetargetDeliveryTo would have been called synchronously from nsJARChannel::OnStartRequest, which would be true if we weren't using a DocumentChannel.

The DocumentLoadListener queue the calls to OnStartRequest until the final redirect.
nsJARChannel::RetargetDelivery mRequest member is be set to forward the call.
So we need to only reset it once OnStopRequest has been received.

Differential Revision: https://phabricator.services.mozilla.com/D70007

modules/libjar/nsJARChannel.cpp

@@ -997,7 +997,6 @@ nsJARChannel::OnStartRequest(nsIRequest* req) {
 
   mRequest = req;
   nsresult rv = mListener->OnStartRequest(this);
-  mRequest = nullptr;
   if (NS_FAILED(rv)) {
     return rv;
   }
@@ -1038,6 +1037,7 @@ nsJARChannel::OnStopRequest(nsIRequest* req, nsresult status) {
 
   if (mLoadGroup) mLoadGroup->RemoveRequest(this, nullptr, status);
 
+  mRequest = nullptr;
   mPump = nullptr;
   mIsPending = false;