Save the "count unread messages" query, when the last read is the last room messages

Signed-off-by: Joas Schilling <coding@schilljs.com>

lib/Controller/RoomController.php

@@ -498,7 +498,13 @@ class RoomController extends AEnvironmentAwareController {
 				$lastReadMessage = $this->chatManager->getLastReadMessageFromLegacy($room, $currentUser);
 				$currentParticipant->setLastReadMessage($lastReadMessage);
 			}
-			$roomData['unreadMessages'] = $this->chatManager->getUnreadCount($room, $lastReadMessage);
+			if ($room->getLastMessage() && $lastReadMessage === (int) $room->getLastMessage()->getId()) {
+				// When the last message is the last read message, there are no unread messages,
+				// so we can save the query.
+				$roomData['unreadMessages'] = 0;
+			} else {
+				$roomData['unreadMessages'] = $this->chatManager->getUnreadCount($room, $lastReadMessage);
+			}
 
 			$lastMention = $currentParticipant->getLastMentionMessage();
 			$roomData['unreadMention'] = $lastMention !== 0 && $lastReadMessage < $lastMention;