month-view: queue redraw on scroll

If we scroll to a month that has no event widget to
display, the redraw is not dispatched and looks like
Calendar is broken.

Fix that by always queuing a redraw.

src/gcal-month-view.c

@@ -970,6 +970,8 @@ gcal_month_view_scroll_event (GtkWidget      *widget,
       *self->date = icaltime_normalize (*self->date);
       self->scroll_value = 0;
 
+      gtk_widget_queue_draw (widget);
+
       g_object_notify (G_OBJECT (widget), "active-date");
     }