st/mesa: small cleanup in st_extensions.c
st/mesa: small cleanup in st_extensions.c

Reviewed-by: Ilia Mirkin <bcbbb7aa705ec3a5fc5824c01a845186c3d62fca@alum.mit.edu>
Reviewed-by: Edward O'Callaghan <eocallaghan at alterapraxis.com>

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler