i965/fs: Fix UB list sentinel dereference in opt_sampler_eot().
i965/fs: Fix UB list sentinel dereference in opt_sampler_eot().

Reviewed-by: Jason Ekstrand <68c46a606457643eab92053c1c05574abb26f861@jlekstrand.net>

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler