Blender Git Loki

Fix T76541: OpenGl Depth Picking not selecting frontmost object

The issue was that we used GL_ALWAYS for depth checking here which would
lead to the depth information from objects being messed up.

It would not represent which object was closest to the camera.

Reviewed By: Cl�ment Foucault, Jeroen Bakker, Campbell Barton

Differential Revision: https://developer.blender.org/D7710