[loss] set zero_infinity=True to ignore NaN or inf ctc_loss

[xingchensong]

• https://pytorch.org/docs/stable/generated/torch.nn.CTCLoss.html
• zero_infinity (bool, optional) – Whether to zero infinite losses and the associated gradients. Default: False Infinite losses mainly occur when the inputs are too short to be aligned to the targets.

Setting zero_infinity=True can help us save a lot of time in data cleaning, as unclean data can be invalidated in the loss calculation through this flag.