Fix padding issues

ml-agents/mlagents/trainers/optimizer/torch_optimizer.py

         for _obs in tensor_obs:
             if leftover > 0:
                 # Pad
-                # _obs will always be bigger than leftover
-                padding = torch.zeros_like(
-                    _obs[0 : self.policy.sequence_length - leftover]
-                )
+                padding_shape = list(_obs.shape)
+                padding_shape[0] = self.policy.sequence_length - leftover
+                padding = torch.zeros(padding_shape)
                 padded_obs = torch.cat([padding, _obs[0:leftover]])
             else:
                 padded_obs = _obs[0 : self.policy.sequence_length]
                 start = seq_num * self.policy.sequence_length - leftover
                 end = (seq_num + 1) * self.policy.sequence_length - leftover
                 seq_obs.append(_obs[start:end])
+                assert _obs[start:end].shape[0] == self.policy.sequence_length
             values, _mem = self.critic.critic_pass(
                 seq_obs, _mem, sequence_length=self.policy.sequence_length
             )