micro-optimization

Co-authored-by: José Valim <jose.valim@gmail.com>

Author: ryanwinchester

lib/phoenix_html/form.ex

@@ -391,7 +391,7 @@ defmodule Phoenix.HTML.Form do
   end
 
   defp option(group_label, group_values, extra, value)
-       when is_list(group_values) or (is_map(group_values) and not is_struct(group_values)) do
+       when is_list(group_values) or (is_map(group_values) and not is_map_key(group_values, :__struct__)) do
     section_options = escaped_options_for_select(group_values, value, extra)
     option_tag("optgroup", [label: group_label], {:safe, section_options})
   end