servo: Merge #17920 - geckolib: Add friendly panic message to Servo_HasAuthorSpecifiedRules (from heycam:hasr-assertion); r=emilio

This just adds a friendlier panic message when `Servo_HasAuthorSpecifiedRules` is called with an unstyled element.

Source-Repo: https://github.com/servo/servo
Source-Revision: 0c9abac373e82b25f2162ddcc3e077c96682a3d7

--HG--
extra : subtree_source : https%3A//hg.mozilla.org/projects/converted-servo-linear
extra : subtree_revision : 5f1eae5e1abc90a7bf36b9e7f4af2dfaaa9d3686

servo/ports/geckolib/glue.rs

@@ -1610,7 +1610,10 @@ pub extern "C" fn Servo_HasAuthorSpecifiedRules(element: RawGeckoElementBorrowed
 {
     let element = GeckoElement(element);
 
-    let data = element.borrow_data().unwrap();
+    let data =
+        element.borrow_data()
+        .expect("calling Servo_HasAuthorSpecifiedRules on an unstyled element");
+
     let primary_style = data.styles.primary();
 
     let guard = (*GLOBAL_STYLE_DATA).shared_lock.read();