[Bug] duration predictor safe guard

[OnceJune]

LightSpeech/core/duration_modeling/length_regulator.py

Line 89 in d9290f7

out.append(x_.repeat(int(d_), 1))

Runtime error when length predicted negative value.
Maybe need to modify to:
out.append(x_.repeat(max(int(d_), 0), 1))

[OnceJune]

and for inference, seems exp and mel to linear is required before sending mel to griffinlim