message: We were putting unexpected empty DataBufferSP's into an array.
  I can't reproduce this so I don't know why we were getting back empty
  data buffers from the underlying llvm calls so I also added logging that
  will tell us what the file was if it happens in the wild.
  <rdar://problem/35393581>
diff: @@ -1481,11 +1481,20 @@ SymbolFileDWARFDebugMap::GetASTData(lldb::LanguageType language) {
  if (file_spec.Exists()) {
  // We found the source data for the AST data blob.
  // Read it in and add it to our return vector.
  - ast_datas.push_back(DataBufferLLVM::CreateFromPath(file_spec.GetPath()));
  + std::shared_ptr<DataBufferLLVM> data_buf_sp
  + = DataBufferLLVM::CreateFromPath(file_spec.GetPath());
  + if (data_buf_sp) {
  + ast_datas.push_back(data_buf_sp);
  if (log)
  log->Printf("SymbolFileDWARFDebugMap::%s() - found and loaded AST "
  "data from file %s",
  __FUNCTION__, file_spec.GetPath().c_str());
  + } else if (log) {
  + if (log)
  + log->Printf("SymbolFileDWARFDebugMap::%s() - got empty data buffer "
  + "SP from extant file %s",
  + __FUNCTION__, file_spec.GetPath().c_str());
  + }
  } else {
  if (log)
  log->Printf("SymbolFileDWARFDebugMap::%s() - found reference to AST "
  