During the execution of 'create table if not exists' DDL query,
ha_ndbcluster::get_default_num_partitions() is called by the
open_table() function implicitly when open_table() finds out that the
requested table already exists. In certain cases
get_default_num_partitions() is called without the thd_ndb object being
seized and initialised. Due to this, the get_default_num_partitions()
reports a HA_ERR_NO_CONNECTION(157) error.

This patch fixes that by checking and initialising the thd_ndb object
always from within ha_ndbcluster::get_default_num_partitions() if it is
not initialised already.