How will the bidirectional flag handle a batch of examples of different sizes?

[horiacristescu]

Hi, I want to use indRNN with batches of examples of different size, but I see this in the repo:

            if self.bidirectional:
                x_T = torch.cat([x, x.flip(-1)], 1)

This makes me think that perhaps the examples are not being flipped properly, because the torch.flip function is applied to the full width tensor.