i965/blorp: Sanity check all layers before actual clear
i965/blorp: Sanity check all layers before actual clear

Signed-off-by: Topi Pohjolainen <749697f19798b7f640b17221fd283b903825f071@intel.com>
Reviewed-by: Jason Ekstrand <68c46a606457643eab92053c1c05574abb26f861@jlekstrand.net>

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler