Don't panic on empty message list

... even though it shouldn't be possible.

crates/core/database/src/tasks/ack.rs

@@ -3,6 +3,7 @@ use crate::{Database, Message, AMQP};
 
 use deadqueue::limited::Queue;
 use once_cell::sync::Lazy;
+use revolt_config::capture_message;
 use revolt_models::v0::PushNotification;
 use std::{
     collections::{HashMap, HashSet},
@@ -64,6 +65,7 @@ pub async fn queue_ack(channel: String, user: String, event: AckEvent) {
     );
 }
 
+/// Do not add more than one message per event.
 pub async fn queue_message(channel: String, event: AckEvent) {
     Q.try_push(Data {
         channel,
@@ -262,15 +264,17 @@ pub async fn worker(db: Database, amqp: AMQP) {
                         if let AckEvent::ProcessMessage { messages: existing } =
                             &mut task.data.event
                         {
-                            // add the new message to the list of messages to be processed.
+                            if let Some(new_event) = new_data.pop() {
-                            existing.append(new_data);
-
                                 // if the message contains a mass mention, do not delay it any further.
-                            if new_data[0].1.contains_mass_push_mention() {
+                                if new_event.1.contains_mass_push_mention() {
+                                    // add the new message to the list of messages to be processed.
+                                    existing.push(new_event);
                                     task.run_immediately();
                                     continue;
                                 }
 
+                                existing.push(new_event);
+
                                 // put a cap on the amount of messages that can be queued, for particularly active channels
                                 if (existing.length() as u16)
                                     < revolt_config::config()
@@ -281,6 +285,11 @@ pub async fn worker(db: Database, amqp: AMQP) {
                                 {
                                     task.delay();
                                 }
+                            } else {
+                                let err_msg = format!("Got zero-length message event: {event:?}");
+                                capture_message(&err_msg, revolt_config::Level::Warning);
+                                info!("{err_msg}")
+                            }
                         } else {
                             panic!("Somehow got an ack message in the add mention arm");
                         }