Make email_send_all() send older queued messages first

To achieve this, a new optional parameter was added to function
email_queue_get_ids() to specify the desired sort order (defaults to
'DESC' to ensure no change in behavior).

email_send_all() now retrieves the list of emails to send in ascending
order.

Fixes #15248

core/email_api.php

@@ -845,7 +845,7 @@ function email_store( $p_recipient, $p_subject, $p_message, $p_headers = null )
  * @return null
  */
 function email_send_all($p_delete_on_failure = false) {
-	$t_ids = email_queue_get_ids();
+	$t_ids = email_queue_get_ids('ASC');
 
 	$t_emails_recipients_failed = array();
 	$t_start = microtime(true);

core/email_queue_api.php

@@ -169,12 +169,13 @@ function email_queue_delete( $p_email_id ) {
 
 /**
  * Get array of email queue id's
+ * @param string $p_sort_order 'ASC' or 'DESC' (defaults to DESC)
  * @return array
  */
-function email_queue_get_ids() {
+function email_queue_get_ids( $p_sort_order = 'DESC' ) {
 	$t_email_table = db_get_table( 'mantis_email_table' );
 
-	$query = 'SELECT email_id FROM ' . $t_email_table . ' ORDER BY email_id DESC';
+	$query = "SELECT email_id FROM $t_email_table ORDER BY email_id $p_sort_order";
 	$result = db_query_bound( $query );
 
 	$t_ids = array();