sampler: pad dry sequence breakers tensor

[AlpinDale]

A potential fix for:

  File "/home/ubuntu/aphrodite-engine/aphrodite/modeling/layers/sampler.py", line 148, in forward
    self._init_sampling_tensors(logits, sampling_metadata)
  File "/home/ubuntu/aphrodite-engine/aphrodite/modeling/layers/sampler.py", line 112, in _init_sampling_tensors
    ) = SamplingTensors.from_sampling_metadata(
        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/ubuntu/aphrodite-engine/aphrodite/modeling/sampling_metadata.py", line 600, in from_sampling_metadata
    sampling_tensors = SamplingTensors.from_lists(
                       ^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/ubuntu/aphrodite-engine/aphrodite/modeling/sampling_metadata.py", line 793, in from_lists
    dry_sequence_breakers_t = torch.tensor(
                              ^^^^^^^^^^^^^
ValueError: expected sequence of length 4 at dim 1 (got 5)

[AlpinDale]

Seems to hold up in production.