Do not disapprove post if another moderator has just approved it

It was brought up by phpBB.com moderators that when two moderators are viewing a post on the moderation queue at the same time and one approves it and then the other disapproves it, the post is deleted; there is no check to make sure the post is still on the queue at the time when an action is performed.

This can result in issues in which one moderator approves the post and replies to the topic and the second moderator disapproves it, leaving the topic without its first post.

This behavior is undesired, imo. Insetad, if the post is not on the moderator queue when the action is triggered, a message should be displayed saying that the post was already approved or disapproved (depending on the action previously taken).