wp_dropdown_categories orderby default 'ID' needs to be lowercase 'id'

[alanft]

problem
&get_terms in taxonomy.php will translate argument orderby 'id' correctly to 't.term_id' (lines 682-683) but will leave ID as is, so the query fails (as there is no ID to order by)

expected outcome
wp_dropdown_categories produces some output - currently it doesn't cos it gets a blank list of categories unless you specify orderby when you call it.

solution
change the default in wp_dropdown_categories (category-template.php) to 'id' (or make the check in taxonomy.php case-insensitive)

[MichaelH]

This seems to be fixed by #9906 and [11428]