Some values were not initialized, causing Valgrind errors (and potential
random bugs):

 - NDB binlog thread thd->variables.pseudo_thread_id.
 - Table null bits.
 - Field bytes for columns with NULL values.


sql/ha_ndbcluster_binlog.cc:
  Fix initialization of thd->variables.pseudo_thread_id.
  Change double alloc_root() call to multi_alloc_root().
  Fix missing initialization of null bits.
sql/sql_class.cc:
  Do not read from the supplied record for NULL values, use the default
  value record instead.
  Otherwise we will get Valgrind errors about uninitialised values written
  to binlog, as NDB does not initialize the memory in records for NULL
  fields.