<?php

function comment_edit_filter() {
	global $pagenow, $comment, $wpdb;

	if ( 'comment.php' != $pagenow )
		return $comment;

	$raw_content = $wpdb->get_var( $wpdb->prepare( "SELECT comment_content FROM $wpdb->comments WHERE comment_ID = %d", $comment->comment_ID ) );
	return esc_html( $raw_content );
}
add_filter( 'the_editor_content', 'comment_edit_filter' );