Fix inverted mesh rendering
Fix inverted mesh rendering

Rendering code for assimp mesh is taken from the examples of assimp (https://github.com/assimp/assimp). There are different use of glEnable(GL_CULL_FACE) and glDisable(GL_CULL_FACE) in the examples. We took incorrect one.

dartsim/dart,dartsim/dart,axeisghost/DART6motionBlur,dartsim/dart,axeisghost/DART6motionBlur,axeisghost/DART6motionBlur,dartsim/dart,dartsim/dart