fix: do not close in ExplainPhysicalOperator

[stevelee477]

What problem were solved in this pull request?

Problem: do not close child operator in ExplainPhysicalOperator

How to reproduce:

create table a (a int);
create index idx on a(a);
explain delete from a where a=1;

cause SegFault, because trying to close IndexScanPhysicalOperator, but not open

What is changed and how it works?

Just do not close child oper in ExplainPhysicalOperator::close

[hnwyllmm]

Thanks