wp_ajax_replyto_comment does not define $comment_type before compact()

[nerrad]

In the wp_ajax_replyto_comment() ajax action callback (wp-admin/includes/ajax-actions.php) compact is called with comment_type as a param. However the variable $comment_type is not defined anywhere. This leads to potential undefined index errors down the chain when it is assumed $commentdata has 'comment_type' ) set.

Patch coming.

[nerrad]

define $comment_type

[wonderboymusic]

In 29758:

In wp_ajax_replyto_comment(), if $_POST['comment_type'] is set, use it for the value of $comment_type, which the compact() call has assumed is set since [8720]. It never was.

wp_comment_reply()'s output can be complete overridden by the wp_comment_reply filter, so this check is justified and makes the AJAX callback more flexible.

Props nerrad.
Fixes #29704.