LibWeb: Keep CSS sheets sorted in document tree order

This ensures that style is applied consistently, even if the document
has external CSS resources that don't always arrive in the same order.

Userland/Libraries/LibWeb/CSS/StyleComputer.cpp

@@ -141,7 +141,7 @@ void StyleComputer::for_each_stylesheet(CascadeOrigin cascade_origin, Callback c
     }
     if (cascade_origin == CascadeOrigin::Author) {
         for (auto const& sheet : document().style_sheets().sheets()) {
-            callback(sheet);
+            callback(*sheet);
         }
     }
 }