[Eva] Fixes the multidim domain on escaping variables and empty structs.

src/plugins/value/domains/multidim/multidim_domain.ml

tests/value/oracle_multidim/empty_struct.0.res.oracle

tests/value/oracle_multidim/empty_struct.1.res.oracle

tests/value/oracle_multidim/empty_struct.2.res.oracle

tests/value/oracle_multidim/empty_struct.3.res.oracle

tests/value/oracle_multidim/empty_struct.5.res.oracle

tests/value/oracle_multidim/empty_struct2.res.oracle

tests/value/oracle_multidim/empty_union.res.oracle

tests/value/oracle_multidim/local.res.oracle

tests/value/oracle_multidim/split_return.0.res.oracle

tests/value/oracle_multidim/split_return.1.res.oracle

tests/value/oracle_multidim/split_return.3.res.oracle

tests/value/oracle_multidim/split_return.4.res.oracle