Suppress unnecessary duration warning

[olaviinha]

Don't show warning if durations are already equal, i.e.

Warning: Duration you specified 10.0-seconds must equal or smaller than the audio file duration 10.0
Set new duration as 12.5-seconds

For example: in the Colab notebook we simulate stereo by applying style transfer to the initial generation for another channel, which is automatically already the same duration, so this warning seems a bit unnecessary.