Fixes 2D picking but not tested with Terrain

[tlpinney]

No description provided.

[pjcozzi]

Thanks @tlpinney. @bagnell can you review? @tlpinney was at the OSGeo code sprint with us.

@tlpinney just a heads up that this is failing JSHint:

[runJsHint] Source/Scene/ImageryLayerCollection.js: line 368, col 24, Expected '===' and instead saw '=='.
[runJsHint] Source/Scene/ImageryLayerCollection.js: line 372, col 32, 'pickedPosition' is already defined.
[runJsHint] Source/Scene/ImageryLayerCollection.js: line 374, col 22, 'pickedPosition' used out of scope.
[runJsHint] Source/Scene/ImageryLayerCollection.js: line 378, col 76, 'pickedPosition' used out of scope.

[tlpinney]

@pjcozzi Thanks. Taking a look now.

[mramato]

Thanks for the pull @tlpinney, but we're doing some PR maintenance and closing this since it's been open forever. I think the real problem is that globe.pick doesn't work in 2D. Your fix works around the imagery picking issue, but doesn't fix the underlying problem. Feel free to re-open this if you want to continue work. Thanks again.