pgsql: Avoid useless allocations for information of dumpable objects in
Avoid useless allocations for information of dumpable objects in pg_dump/
If there are no objects of a certain type, there is no need to do an
allocation for a set of DumpableObject items. The previous coding did
an allocation of 1 byte instead as per the fallback of pg_malloc() in
the event of an allocation size of zero. This assigns NULL instead for
a set of dumpable objects.
A similar rule already applied to findObjectByOid(), so this makes the
code more defensive as we would just fail with a pointer dereference
instead of attempting to use some incorrect data if a non-existing,
positive, OID is given by a caller of this function.