osgearth_featureditor sample crashes when editing

[beachwalker]

The feature editor sample allows adding lines but crushes when switching to edit mode.

• first add verts
• create some lines
• click the button for switching to edit mode => crush

environment: x64, windows 8, no qt

[beachwalker]

Seems to be there is a duplicate: https://github.com/gwaldron/osgearth/issues/564

[gwaldron]

yep, thanks - closed for dupe