analyzer: fix ignored constraints involving casts [PR113619]

gcc/analyzer/ChangeLog:
	PR analyzer/113619
	* region-model.cc (region_model::eval_condition): Fix
	cast-handling from r14-3632-ge7b267444045c5 so that if those give
	an unknown result, we continue trying the constraint manager.

gcc/testsuite/ChangeLog:
	PR analyzer/113619
	* c-c++-common/analyzer/taint-divisor-pr113619.c: New test.

Signed-off-by: David Malcolm <dmalcolm@redhat.com>