PyBullet change API (since it was broken): pybullet_changeVisualShape with textureUniqueId ==-1 will clear the texture

b3InitUpdateVisualShape doesn't take textureUniqueId by default. new API b3UpdateVisualShapeTexture to change texture (-1 will clear texture)
PyBullet/BulletRobotics: allow to reset the textureUniqueId to -1, to clear a texture
PyBullet/BulletRobotics: save all texture handles

examples/OpenGLWindow/GLInstancingRenderer.cpp

@@ -1009,6 +1009,10 @@ void GLInstancingRenderer::replaceTexture(int shapeIndex, int textureId)
 		{
 			gfxObj->m_textureIndex = textureId;
 			gfxObj->m_flags |= eGfxHasTexture;
+		} else
+		{
+			gfxObj->m_textureIndex = -1;
+			gfxObj->m_flags &= ~eGfxHasTexture;
 		}
 	}
 }