isl_map_zip: add missing isl_map_unmark_normalized
isl_map_zip: add missing isl_map_unmark_normalized

Changing the order of the dimensions may change the sorting
order of the basic maps within the map, so the result
of the zip can no longer be assumed to be normalized.

Signed-off-by: Sven Verdoolaege <dd860110a62b19214c4ee03aec0abffecb4e86b8@cerebras.net>

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