isl_basic_{set,map}_read_*: improve error message
isl_basic_{set,map}_read_*: improve error message

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

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