Use default schema if $tableName has no namespace.

[kitloong]

Q	A
Type	bug

Summary

When 2 same name tables exist in difference schema, eg: public.table and another.table, $this->schemaManager->listTableColumns('table') will list and mix columns from both tables.

I have confirmed listTableColumns is working correctly before #5586.
This PR fixes the column issue while respecting #5586 listTables fix.

Steps to reproduce

create table public."table"
(
    id   integer not null,
    name text    not null
);

create table another."table"
(
    id    text not null,
    email text not null
);

Run $this->schemaManager->listTableColumns('table')

Actual

List table columns mixed from public and another schema.

[
   'id', // text, override by another."table"
   'name', // text
   'email', // text, merged from another."table"
]

Expected

List table columns from the public schema only.

[
   'id', // integer
   'name', // text
]

[morozov]

Thanks, @kitloong.