isl_fold.c: avoid warning about control reaching end of non-void function
isl_fold.c: avoid warning about control reaching end of non-void function

Based on a patch by Tobias Grosser <tobias@grosser.es>.

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

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