resolve panic when extending certain psuedo selectors containing combinators without rhs selector

src/selector/extend/functions.rs

@@ -186,7 +186,13 @@ fn weave_parents(
     for group in lcs {
         choices.push(
             chunks(&mut groups_one, &mut groups_two, |sequence| {
-                complex_is_parent_superselector(sequence.get(0).unwrap().clone(), group.clone())
+                complex_is_parent_superselector(
+                    match sequence.get(0) {
+                        Some(v) => v.clone(),
+                        None => return true,
+                    },
+                    group.clone(),
+                )
             })
             .into_iter()
             .map(|chunk| chunk.into_iter().flatten().collect())

tests/extend.rs

@@ -1874,6 +1874,14 @@ test!(
     }",
     "foo, a:current(foo),\n:current(foo) {\n  color: black;\n}\n"
 );
+test!(
+    extend_pseudo_selector_class_containing_combinator_without_rhs_selector,
+    ":has(a >) b {
+        @extend b;
+        color: red;
+    }",
+    ":has(a >) b, :has(a >) :has(a >) :has(a >) b, :has(a >) :has(a >) :has(a >) b {\n  color: red;\n}\n"
+);
 
 // todo: extend_loop (massive test)
 // todo: extend tests in folders