isl_dim_total: handle NULL input
isl_dim_total: handle NULL input

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

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