Auto merge of #23021 - ejmg:assert_fail_#18439, r=jdm

Assert fail #18439

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This PR addresses #18439 by removing an assert statement that forces a panic whenever `LoadBlocker` is dropped during a GC sweep and receives a `None` `SCRIPT_THREAD_ROOT` value from `mark_document_with_no_blocked_loads()`. Instead of panicking on the assert, we remove it and let the None value pass silently.

---
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- [x] `./mach build -d` does not report any errors
- [x] `./mach test-tidy` does not report any errors
- [x] These changes fix #18439

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- [ ] There are tests for these changes OR
- [ ] These changes do not require tests because ___

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components/script/document_loader.rs

@@ -14,7 +14,6 @@ use net_traits::request::RequestInit;
 use net_traits::{CoreResourceMsg, FetchChannels, FetchResponseMsg};
 use net_traits::{IpcSend, ResourceThreads};
 use servo_url::ServoUrl;
-use std::thread;
 
 #[derive(Clone, Debug, JSTraceable, MallocSizeOf, PartialEq)]
 pub enum LoadType {
@@ -77,8 +76,8 @@ impl LoadBlocker {
 
 impl Drop for LoadBlocker {
     fn drop(&mut self) {
-        if !thread::panicking() {
-            debug_assert!(self.load.is_none());
+        if let Some(load) = self.load.take() {
+            self.doc.finish_load(load);
         }
     }
 }

components/script/script_thread.rs

@@ -809,11 +809,13 @@ impl ScriptThread {
 
     pub fn mark_document_with_no_blocked_loads(doc: &Document) {
         SCRIPT_THREAD_ROOT.with(|root| {
-            let script_thread = unsafe { &*root.get().unwrap() };
-            script_thread
-                .docs_with_no_blocking_loads
-                .borrow_mut()
-                .insert(Dom::from_ref(doc));
+            if let Some(script_thread) = root.get() {
+                let script_thread = unsafe { &*script_thread };
+                script_thread
+                    .docs_with_no_blocking_loads
+                    .borrow_mut()
+                    .insert(Dom::from_ref(doc));
+            }
         })
     }