Auto merge of #15334 - canaltinova:inverse, r=nox

Fix the panic when transform is non-invertible

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Fixes the panic when transform is non-invertible.
Counterpart of https://github.com/servo/webrender/pull/823
r? @glennw

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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 #13266 (github issue number if applicable).

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- [ ] These changes do not require tests because _____

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components/gfx/display_list/mod.rs

@@ -182,7 +182,14 @@ impl DisplayList {
             *client_point
         } else {
             let point = *translated_point - stacking_context.bounds.origin;
-            let inv_transform = stacking_context.transform.inverse().unwrap();
+            let inv_transform = match stacking_context.transform.inverse() {
+                Some(transform) => transform,
+                None => {
+                    // If a transform function causes the current transformation matrix of an object
+                    // to be non-invertible, the object and its content do not get displayed.
+                    return;
+                }
+            };
             let frac_point = inv_transform.transform_point(&Point2D::new(point.x.to_f32_px(),
                                                                          point.y.to_f32_px()));
             Point2D::new(Au::from_f32_px(frac_point.x), Au::from_f32_px(frac_point.y))