Handle empty function type in fun_apply

Closes #15486.

Author: josevalim

lib/elixir/lib/module/types/descr.ex

@@ -1560,6 +1560,9 @@ defmodule Module.Types.Descr do
             {:badarity, [arity | other]}
         end
 
+      :badfun when fun_dynamic == nil ->
+        :badfun
+
       :badfun ->
         # No static arrows: dynamic-only path. Mixed-arity in the dynamic
         # component is fine — we pick the matching-arity arrows and the

lib/elixir/test/elixir/module/types/descr_test.exs

@@ -1197,6 +1197,7 @@ defmodule Module.Types.DescrTest do
     test "non funs" do
       assert fun_apply(term(), [integer()]) == :badfun
       assert fun_apply(integer(), [integer()]) == :badfun
+      assert fun_apply(none(), [integer()]) == :badfun
       assert fun_apply(union(integer(), none_fun(1)), [integer()]) == :badfun
       assert fun_apply(union(integer(), fun([integer()], atom())), [integer()]) == :badfun
       assert fun_apply(union(integer(), dynamic()), [integer()]) == :badfun