Auto merge of #12277 - ConnorGBrewster:network_listener_cancellable, r=Manishearth

Make network listener runnable cancellable

<!-- Please describe your changes on the following line: -->
This keeps scripts from executing after its script thread has been shut down.

---
<!-- Thank you for contributing to Servo! Please replace each `[ ]` by `[X]` when the step is complete, and replace `__` with appropriate data: -->
- [X] `./mach build -d` does not report any errors
- [X] `./mach test-tidy` does not report any errors
- [x] These changes fix (maybe) #12048 (github issue number if applicable).

<!-- Either: -->
- [X] There are tests for these changes OR
- [ ] These changes do not require tests because _____

<!-- Pull requests that do not address these steps are welcome, but they will require additional verification as part of the review process. -->

<!-- Reviewable:start -->
---
This change is [<img src="https://reviewable.io/review_button.svg" height="35" align="absmiddle" alt="Reviewable"/>](https://reviewable.io/reviews/servo/servo/12277)
<!-- Reviewable:end -->

1 files changed, 1 insertions, 0 deletions

diff --git a/components/script/dom/xmlhttprequest.rs b/components/script/dom/xmlhttprequest.rs
index e76bbd0c7b3..148a51c8c6b 100644
--- a/components/script/dom/xmlhttprequest.rs
+++ b/components/script/dom/xmlhttprequest.rs
@@ -258,6 +258,7 @@ impl XMLHttpRequest {
         let listener = NetworkListener {
             context: context,
             script_chan: script_chan,
+            wrapper: None,
         };
         ROUTER.add_route(action_receiver.to_opaque(), box move |message| {
             listener.notify_fetch(message.to().unwrap());