fix empty CHATHISTORY TARGETS

Currently, if times sent to `CHATHISTORY TARGETS` are reversed (e.g.
current time occurs first, and initial time occurs second) then no
targets will be returned from the database backend.

Changes have been tested with the sqlite backend.

msgstore/db.go

@@ -89,12 +89,24 @@ func (ms *dbMessageStore) Append(network *database.Network, entity string, msg *
 }
 
 func (ms *dbMessageStore) ListTargets(ctx context.Context, network *database.Network, start, end time.Time, limit int, events bool) ([]ChatHistoryTarget, error) {
-	l, err := ms.db.ListMessageLastPerTarget(ctx, network.ID, &database.MessageOptions{
+	var opts  *database.MessageOptions
+	if start.Before(end) {
+		opts = &database.MessageOptions{
 			AfterTime:  start,
 			BeforeTime: end,
 			Limit:      limit,
 			Events:     events,
-	})
+		}
+	} else {
+		opts = &database.MessageOptions{
+			AfterTime:  end,
+			BeforeTime: start,
+			Limit:      limit,
+			Events:     events,
+			TakeLast: true,
+		}
+	}
+	l, err := ms.db.ListMessageLastPerTarget(ctx, network.ID, opts);
 	if err != nil {
 		return nil, err
 	}