[pg] Fix INTERNAL ERROR for psql `\d` command - list tables

[rekby]

Reproduce:

1. Run local_ydb with postgres experiment enabled https://github.com/ydb-platform/ydb/wiki/Local-run-postgres-tests
2. Connect to YDB with psql: psql postgres://root:1234@localhost:5432/local
3. echo '\d' | psql postgres://root:1234@localhost:5432/local

Query from psql

``` SELECT n.nspname as "Schema", c.relname as "Name", CASE c.relkind WHEN 'r' THEN 'table' WHEN 'v' THEN 'view' WHEN 'm' THEN 'materialized view' WHEN 'i' THEN 'index' WHEN 'S' THEN 'sequence' WHEN 's' THEN 'special' WHEN 't' THEN 'TOAST table' WHEN 'f' THEN 'foreign table' WHEN 'p' THEN 'partitioned table' WHEN 'I' THEN 'partitioned index' END as "Type", pg_catalog.pg_get_userbyid(c.relowner) as "Owner" FROM pg_catalog.pg_class c LEFT JOIN pg_catalog.pg_namespace n ON n.oid = c.relnamespace LEFT JOIN pg_catalog.pg_am am ON am.oid = c.relam WHERE c.relkind IN ('r','p','v','m','S','f','') AND n.nspname <> 'pg_catalog' AND n.nspname !~ '^pg_toast' AND n.nspname <> 'information_schema' AND pg_catalog.pg_table_is_visible(c.oid) ORDER BY 1,2; ```

Error

``` Status: INTERNAL_ERROR Issues:

: Fatal: ydb/library/yql/parser/pg_wrapper/comp_factory.cpp:456: Condition violated: `f', code: 1

: Error: Query invalidated on scheme/internal error., code: 2019 ```

[vitstn]

with PR:

local=> \d Did not find any relations.