vrend: Do not unconditionally use TEXTURE_CUBE_MAP_SEAMLESS with glSamplerParameteri
In case the ARB_seamless_cubemap_per_texture isn't available it is not possible to use TEXTURE_CUBE_MAP_SEAMLESS with glSamplerParameteri.
In case the ARB_seamless_cubemap_per_texture isn't available it is not possible to use TEXTURE_CUBE_MAP_SEAMLESS with glSamplerParameteri.