isl_basic_map_gist: avoid invalid access on error path
isl_basic_map_gist: avoid invalid access on error path

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

jleben/isl,nicolasvasilache/isl,Meinersbur/isl,PollyLabs/isl,nicolasvasilache/isl,BenzoSM/isl,cfx-next/toolchain_isl-upstream,VanirLLVM/toolchain_isl,nicolasvasilache/isl,crossbuild/isl,UBERTC/isl,serge-sans-paille/isl,KangDroidSMProject/ISL,jleben/isl,inducer/isl-mirror,Distrotech/isl,PollyLabs/isl,BobSaget-Mod/libisl,jleben/isl,PollyLabs/isl,BobSaget-Mod/libisl,BobSaget-Mod/libisl,cfx-next/toolchain_isl-upstream,evaautomation/isl,evaautomation/isl,inducer/isl-mirror,UBERTC/isl,UBERTC/isl,crossbuild/isl,serge-sans-paille/isl,abduld/isl,Distrotech/isl,tobig/isl,cfx-next/toolchain_isl-upstream,crossbuild/isl,simbuerg/isl,BenzoSM/isl,SaberMod/isl-current,BenzoSM/isl,serge-sans-paille/isl,evaautomation/isl,UBERTC/isl,cfx-next/toolchain_isl-upstream,jleben/isl,abduld/isl,BobSaget-Mod/libisl,jleben/isl,PollyLabs/isl,SaberMod/isl-current,tobig/isl,evaautomation/isl,SaberMod/isl-current,Distrotech/isl,simbuerg/isl,nicolasvasilache/isl,Meinersbur/isl,BenzoSM/isl,abduld/isl,tobig/isl,KangDroidSMProject/ISL,KangDroidSMProject/ISL,simbuerg/isl,inducer/isl-mirror,inducer/isl-mirror,VanirLLVM/toolchain_isl,BenzoSM/isl,Distrotech/isl,Meinersbur/isl,PollyLabs/isl,serge-sans-paille/isl,abduld/isl,inducer/isl-mirror,VanirLLVM/toolchain_isl,KangDroidSMProject/ISL,Distrotech/isl,simbuerg/isl,BobSaget-Mod/libisl,VanirLLVM/toolchain_isl,serge-sans-paille/isl,cfx-next/toolchain_isl-upstream,KangDroidSMProject/ISL,simbuerg/isl,crossbuild/isl,nicolasvasilache/isl,VanirLLVM/toolchain_isl,tobig/isl,SaberMod/isl-current,Meinersbur/isl