isl_tab_pip.c: context_tab_for_lexmin: plug memory leak on error path
isl_tab_pip.c: context_tab_for_lexmin: plug memory leak on error path

If isl_tab_track_bset fails, then only the associated basic set would
be freed, but not the containing isl_tab.
Let isl_tab_track_bset consume the basic set and free the isl_tab
in case of error.

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

PollyLabs/isl,Meinersbur/isl,tobig/isl,Meinersbur/isl,nicolasvasilache/isl,PollyLabs/isl,nicolasvasilache/isl,inducer/isl-mirror,tobig/isl,inducer/isl-mirror,tobig/isl,inducer/isl-mirror,tobig/isl,nicolasvasilache/isl,Meinersbur/isl,PollyLabs/isl,PollyLabs/isl,Meinersbur/isl,inducer/isl-mirror,nicolasvasilache/isl,nicolasvasilache/isl,inducer/isl-mirror,PollyLabs/isl