isl_basic_map_plain_is_equal: improve error handling
isl_basic_map_plain_is_equal: improve error handling

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

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