isl_basic_map_plain_unshifted_simple_hull: check inputs live in same space
isl_basic_map_plain_unshifted_simple_hull: check inputs live in same space

This was missing from the initial implementation.
The condition is currently always satisfied because
isl_basic_map_plain_unshifted_simple_hull is only called
on basic maps from the same map, but this function may
get exposed in the future.

Signed-off-by: Sven Verdoolaege <235c10dd23b819f81cdc9756a251746bc184cab6@gmail.com>

Meinersbur/isl,Meinersbur/isl,Meinersbur/isl,Meinersbur/isl