[ticket/11842] Use group_id 0 and correct avatar name after creating group

It seems like the function group_correct_avatar() was forgotten while adding
the new avatar system. We now pass the group_id 0 to the upload avatar and
let the function group_correct_avatar() fix the avatar filename after creating
the group like it was done previously.

PHPBB3-11842

phpBB/includes/acp/acp_groups.php

@@ -325,6 +325,10 @@ class acp_groups
 
 					// This is normalised data, without the group_ prefix
 					$avatar_data = \phpbb\avatar\manager::clean_row($group_row);
+					if (!isset($avatar_data['id']))
+					{
+						$avatar_data['id'] = $group_id;
+					}
 				}