gl2d changing dragmode doesn't take effect immediately

Changing dragmode in the modebar doesn't take effect until a full redraw (autoscale, for example).
- Open https://codepen.io/etpinard/pen/mojEWY?editors=111
- Change from zoom to pan
- Try to pan - you actually zoom
- Click the autoscale, zoom in, or zoom out button to trigger a redraw
- Now you can pan - but if you change to zoom you'll be stuck panning.