Fix: the 'smgropen' in the 'calculate_relation_size' function may return an incorrect 'smgrRelation'

[Lzjing-1997]

steps to reproduce:

postgres=# create table sa(a int) partition by range(a);
CREATE TABLE
postgres=# create unlogged table sb(b int) partition by range(b);
CREATE TABLE
postgres=# select pg_relation_size('sa'), pg_relation_size('sb');
ERROR: relpersistence mismatch: smgropen u vs SmgrRelation p

For a partitioned table, the relfilenode of its parent table is always 0 ; 'smgropen' in function 'calculate_relation_size' may get incorrect 'smgrRelation' due to 'SMgrRelationHash'.

[tristan957]

I have created a team task for us to review your PR. Thanks for contributing!