Bugfix: code breaks if audio is empty

[Purfview]

Regression since #732 PR [Improve language detection]

Bug can happen if VAD didn't found voice in audio.
Bugfix brings back the previous behaviour on empty audio.

[trungkienbkhn]

@Purfview , thanks for your findings. However, I think that it can revert to its previous behavior with a simple logic outlined below (seek <= content_frames):

while (
    seek <= content_frames
    and seek
    < self.feature_extractor.nb_max_frames * language_detection_segments
)

[Purfview]

Yes, seek <= content_frames is simpler fix, thx.