use existing constant

Signed-off-by: Andy Scherzinger <info@andy-scherzinger.de>

app/src/main/java/com/nextcloud/talk/controllers/ChatController.kt

@@ -2538,7 +2538,7 @@ class ChatController(args: Bundle) :
             menu.findItem(R.id.action_delete_message).isVisible = isShowMessageDeletionButton(message)
             menu.findItem(R.id.action_forward_message).isVisible =
                 ChatMessage.MessageType.REGULAR_TEXT_MESSAGE == message.getMessageType()
-            menu.findItem(R.id.action_mark_as_unread).isVisible = message.previousMessageId > -1 &&
+            menu.findItem(R.id.action_mark_as_unread).isVisible = message.previousMessageId > NO_PREVIOUS_MESSAGE_ID &&
                 ChatMessage.MessageType.SYSTEM_MESSAGE != message.getMessageType()
             if (menu.hasVisibleItems()) {
                 if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.Q) {