message: Implement blank_index parameter in ctc_greedy_decoder
  Added blank_index as parameter in ctc_greedy_decoder
  Only accepting positive number
diff: @@ -329,11 +329,14 @@ def ctc_greedy_decoder(inputs,
  timeframe.
  """
  - if blank_index is None:
  - blank_index = _get_dim(inputs, 2)
  + if blank_index is not None:
  + part_before = inputs[:, :, :blank_index]
  + part_after = inputs[:, :, blank_index + 1:]
  + part_blank = inputs[:, :, blank_index:blank_index + 1]
  + inputs = array_ops.concat([part_before, part_after, part_blank], axis=2)
  outputs = gen_ctc_ops.ctc_greedy_decoder(
  - inputs, sequence_length, merge_repeated=merge_repeated, blank_index=blank_index)
  + inputs, sequence_length, merge_repeated=merge_repeated)
  (decoded_ix, decoded_val, decoded_shape, log_probabilities) = outputs
  return ([sparse_tensor.SparseTensor(decoded_ix, decoded_val,
  decoded_shape)], log_probabilities)
  