Fixed Bug #64949 (Buffer overflow in _pdo_pgsql_error)

There is a lot of call such as:
	pdo_pgsql_error(dbh, PGRES_FATAL_ERROR, "Copy command failed");
Where the 3rd paramater is a error message string where a sqlstate (5 chars)
is expected. This cause a segfault in copy_from.phpt and copy_to.phpt.

This is only a sanity check to avoid buffer overflow, but obviously this
calls need to be fixed (using NULL or a correct sqlstate).