gbm: Assert modifiers and count are copacetic
gbm: Assert modifiers and count are copacetic

The API/entry point in mesa already checks the correct behavior,
however, it's possible to be handled by another implementation and those
implementations should not be able to abuse a weird combination of count
and pointer.

This fixes CID 1403193

Cc: Mark Janes <dc19c7a5044e1b627d35321fa5e1121fad8638f9@intel.com>
Signed-off-by: Ben Widawsky <73675debcd8a436be48ec22211dcf44fe0df0a64@bwidawsk.net>
Reviewed-by: Jason Ekstrand <68c46a606457643eab92053c1c05574abb26f861@jlekstrand.net>

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler