Check/reset OpenGL error state for render chains

[straubar]

Not all modules explicitly check the OpenGL error state after doing their usual stuff. This can, e.g., lead to raised exceptions elsewhere when the state is checked. To mitigate this to some extent, it might be a good idea to check and thus reset the error state in the chain render functions, i.e., somewhere in the final functions GetExtentsChain and RenderChain of the RendererXDModuleGL modules.