Fix: always update the most recent help status

The message cache does not have a stable order (I suspect it is simply
the order in which the messages were added to the cache). Thus, when
searching for the latest status message, sometimes a message other than
the latest was picked.

In practice, it seems like this only ever happened when the bot was
offline for a number of hours, which is why it hasn't come up in
production. But in development, it could be reproduced by:

- Leave the bot offline for a while (24h?)
- Start the bot
- Claim a channel
- The channel that is moved up from being dormant has the wrong message
  edited, so the message at the bottom still says "dormant".

I suspect this is what the `.reverse()`, which was removed in commit
09ad491, was intended to solve (but it
caused bugs during normal operation). This should be a full fix.

I am not sure of the performance implications here. I think it should
not be too bad, because we are filtering to only messages from the bot,
before sorting.

Author: smichel17

src/modules/helpchan.ts

@@ -346,12 +346,16 @@ export class HelpChanModule extends Module {
 				this.DORMANT_EMBED.title,
 			].includes(embed.title);
 
+		// The message cache does not have a stable order (at least with respect
+		// to creation date), so sorting is needed to find the latest embed.
 		let lastMessage = channel.messages.cache
 			.array()
 			.filter(m => m.author.id === this.client.user?.id)
+			.sort((m1, m2) => m2.createdTimestamp - m1.createdTimestamp)
 			.find(m => m.embeds.some(isStatusEmbed));
 
 		if (!lastMessage)
+			// Fetch has a stable order, with recent messages first
 			lastMessage = (await channel.messages.fetch({ limit: 5 }))
 				.array()
 				.filter(m => m.author.id === this.client.user?.id)