isl_tab_add_eq: explicitly initialize constant term
isl_tab_add_eq: explicitly initialize constant term

All current backends initialize an isl_int to 0 by default,
but it is safer to perform the initialization explicitly.

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

PollyLabs/isl,BenzoSM/isl,inducer/isl-mirror,nicolasvasilache/isl,PollyLabs/isl,inducer/isl-mirror,tobig/isl,Meinersbur/isl,BenzoSM/isl,Distrotech/isl,PollyLabs/isl,BenzoSM/isl,PollyLabs/isl,UBERTC/isl,PollyLabs/isl,UBERTC/isl,inducer/isl-mirror,tobig/isl,nicolasvasilache/isl,Distrotech/isl,nicolasvasilache/isl,BenzoSM/isl,inducer/isl-mirror,UBERTC/isl,Distrotech/isl,inducer/isl-mirror,Meinersbur/isl,Meinersbur/isl,Distrotech/isl,Meinersbur/isl,UBERTC/isl,tobig/isl,tobig/isl,nicolasvasilache/isl,nicolasvasilache/isl,Distrotech/isl,BenzoSM/isl