with blobs containing nulls

Problem: FEDERATED SE improperly stores NULL fields in the record buffer.

Fix: store them properly.


mysql-test/r/federated.result:
  Fix for bug #34779: crash in checksum table on federated tables 
  with blobs containing nulls
    - test result.
mysql-test/t/federated.test:
  Fix for bug #34779: crash in checksum table on federated tables 
  with blobs containing nulls
    - test case.
sql/ha_federated.cc:
  Fix for bug #34779: crash in checksum table on federated tables 
  with blobs containing nulls
    - storing a NULL field in the record buffer
      we must initialize its data as other code
      may rely on it.