Snapping sample in OpenLayers 2.8 doesn't work in Chrome and Safari

[Mars Wu]

Steps to reproduce

- Run the 2.8 release snapping sample ( http://dev.openlayers.org/releases/OpenLayers-2.8/examples/snapping.html) in Chrome or Safari.

- Click "Modify features" tool button

- Select a polygon to make it into "edit mode"

- Drag and move a grip point for a while

Results:

Unhandled exception happened which will make Chrome display a blue "Aw, Snap" screen and Safari bring up an unhandled exception dialog.

[fredj]

see #2402