patch 9.0.1605: crash when calling method on super in child constructor

Problem:    Crash when calling method on super in child constructor. (Israel
            Chauca Fuentes)
Solution:   Clear the type list. (Ernie Rael, closes #12489, closes #12471)

src/testdir/test_vim9_class.vim

@@ -1636,6 +1636,28 @@ def Test_using_base_class()
   END
   v9.CheckScriptSuccess(lines)
   unlet g:result
+
+  # Using super, Child invokes Base method which has optional arg. #12471
+  lines =<< trim END
+    vim9script
+
+    class Base
+        this.success: bool = false
+        def Method(arg = 0)
+            this.success = true
+        enddef
+    endclass
+
+    class Child extends Base
+        def new()
+            super.Method()
+        enddef
+    endclass
+
+    var obj = Child.new()
+    assert_equal(true, obj.success)
+  END
+  v9.CheckScriptSuccess(lines)
 enddef