isl_convex_hull.c: convex_hull_pair_pointed: use isl_basic_set_get_ctx
isl_convex_hull.c: convex_hull_pair_pointed: use isl_basic_set_get_ctx

Do so instead of looking into isl_basic_set internals.

Signed-off-by: Sven Verdoolaege <e5350bbed4977f5eb8ae1dc6abd9ae59d21ace75@kotnet.org>

KangDroidSMProject/ISL,nicolasvasilache/isl,Distrotech/isl,tobig/isl,KangDroidSMProject/ISL,PollyLabs/isl,Meinersbur/isl,simbuerg/isl,SaberMod/isl-current,Meinersbur/isl,nicolasvasilache/isl,abduld/isl,tobig/isl,Distrotech/isl,BenzoSM/isl,PollyLabs/isl,KangDroidSMProject/ISL,evaautomation/isl,abduld/isl,KangDroidSMProject/ISL,tobig/isl,UBERTC/isl,Meinersbur/isl,nicolasvasilache/isl,BenzoSM/isl,inducer/isl-mirror,simbuerg/isl,simbuerg/isl,abduld/isl,SaberMod/isl-current,Distrotech/isl,Meinersbur/isl,inducer/isl-mirror,UBERTC/isl,SaberMod/isl-current,BenzoSM/isl,inducer/isl-mirror,Distrotech/isl,abduld/isl,BenzoSM/isl,nicolasvasilache/isl,UBERTC/isl,tobig/isl,evaautomation/isl,PollyLabs/isl,UBERTC/isl,PollyLabs/isl,inducer/isl-mirror,PollyLabs/isl,simbuerg/isl,inducer/isl-mirror,KangDroidSMProject/ISL,BenzoSM/isl,simbuerg/isl,Distrotech/isl,evaautomation/isl,evaautomation/isl,SaberMod/isl-current,nicolasvasilache/isl