message: walletdb: Ensure that having no database handle is a failure
  Previously having no database handle could still be considered a success
  when BerkeleyDatabase and BerkeleyBatch were used for dummy database
  things. With dedicated DummyDatabase and DummyBatch classes now, these
  should fail.
diff: @@ -767,7 +767,7 @@ bool BerkeleyBatch::ReadKey(CDataStream&& key, CDataStream& value)
  bool BerkeleyBatch::WriteKey(CDataStream&& key, CDataStream&& value, bool overwrite)
  {
  if (!pdb)
  - return true;
  + return false;
  if (fReadOnly)
  assert(!"Write called on database in read-only mode");
  