state: add filling out BeforeDelete before deleting message

state.go

@@ -893,6 +893,13 @@ func (s *State) OnInterface(se *Session, i interface{}) (err error) {
 		}
 	case *MessageDelete:
 		if s.MaxMessageCount != 0 {
+			var old *Message
+			old, err = s.Message(t.ChannelID, t.ID)
+			if err == nil {
+				oldCopy := *old
+				t.BeforeDelete = &oldCopy
+			}
+
 			err = s.MessageRemove(t.Message)
 		}
 	case *MessageDeleteBulk: