Fixes assertion error when using _--reportalign by passing _src_padmask and _tgt_padmask to decoder
File "~/eole/eole/decoders/transformer_decoder.py", line 180, in forward
assert tgt_pad_mask is not None, "TransformerDecoder requires a tgt pad mask"
AssertionError: TransformerDecoder requires a tgt pad mask
Fixes assertion error when using _--reportalign by passing _src_padmask and _tgt_padmask to decoder