Auto merge of #18603 - tigercosmos:allocating, r=KiChjang

fix #18594: Unnecessarily allocating an error string

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r? @asajeffrey

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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 #18594 (github issue number if applicable).

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components/script/document_loader.rs

@@ -130,7 +130,7 @@ impl DocumentLoader {
     pub fn finish_load(&mut self, load: &LoadType) {
         debug!("Removing blocking load {:?} ({}).", load, self.blocking_loads.len());
         let idx = self.blocking_loads.iter().position(|unfinished| *unfinished == *load);
-        self.blocking_loads.remove(idx.expect(&format!("unknown completed load {:?}", load)));
+        self.blocking_loads.remove(idx.unwrap_or_else(|| panic!("unknown completed load {:?}", load)));
     }
 
     pub fn is_blocked(&self) -> bool {