message: Fix Lucene TM export to iterate all docs
  Fix code for iterating Lucene index to use maxDoc() instead of
  numDocs(). The former is guaranteed to be larger than the largest
  document index present, the latter is not. Necessitates the use of
  isDeleted() check too.
  See
diff: @@ -559,9 +559,11 @@ void TranslationMemoryImpl::ExportData(TranslationMemory::IOInterface& destinati
  try
  {
  auto reader = m_mng->Reader();
  - int32_t numDocs = reader->numDocs();
  + int32_t numDocs = reader->maxDoc();
  for (int32_t i = 0; i < numDocs; i++)
  {
  + if (reader->isDeleted(i))
  + continue;
  auto doc = reader->document(i);
  destination.Insert
  (
  