isl_map_from_pw_aff: handle NULL input
isl_map_from_pw_aff: handle NULL input

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

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