OpenGL SamplerState had null GraphicsDevice
The GraphicsDevice had never been set in the OpenGL version of SamplerState. This PR sets it and checks for the SamplerState being used on the same GraphicsDevice as it was first used, similar to the DirectX version.
Merge pull request #2858 from KonajuGames/samplerstate-opengl-graphicsdevice

OpenGL SamplerState had null GraphicsDevice