message: fix var type issue which breaks crf_decode
  CRF decode can fail when default type of "0" (as viewed by math_ops.maximum) does not match the type of sequence_length.
  This change is parallel in motivation and solution to the fix in for crf_log_norm()=>_multi_seq_fn().
diff: @@ -548,7 +548,9 @@ def crf_decode(potentials, transition_params, sequence_length):
  initial_state = array_ops.squeeze(initial_state, axis=[1]) # [B, O]
  inputs = array_ops.slice(potentials, [0, 1, 0], [-1, -1, -1]) # [B, T-1, O]
  # Sequence length is not allowed to be less than zero.
  - sequence_length_less_one = math_ops.maximum(0, sequence_length - 1)
  + sequence_length_less_one = math_ops.maximum(
  + constant_op.constant(0, dtype=sequence_length.dtype),
  + sequence_length - 1)
  backpointers, last_score = rnn.dynamic_rnn( # [B, T - 1, O], [B, O]
  crf_fwd_cell,
  inputs=inputs,
  