BibIndex: filetype and itemcount tokenizer fix

* Filetype and itemcount tokenizers now correctly
  handle TypeError in cases when they were passed
  object different than bibfield's record.
  (closes #1609)

Reported-by: Theodoropoulos Theodoros <theod@lib.auth.gr>
Signed-off-by: Grzegorz Szpura <grzegorz.szpura@cern.ch>
Reviewed-by: Tibor Simko <tibor.simko@cern.ch>