If ::exteral_lock hadn't been called, we'd have no NDB object,
so need to check/get one here.

It looks like sql_show.cc is the only place that does this....
or at least the other places will be well hidden.

Index: ndb-work/sql/ha_ndbcluster.cc
===================================================================


sql/ha_ndbcluster.cc:
  Bug#26793 I_S query crashes in NDB