[seamlisten] bug: padding is added to segments without the grey area to indicate it

[Celebio]

When displaying single segments in seamliten the padding is added to the segment without being highlighted.

To reproduce paste this segment in seamlisten

/path/to/audio/some.mp3 1917117 1962282

to verify that its longer than the original segment here's how to listen to the segment
paste the following command in a notebook

  import librosa 
  import IPython.display as ipd
  
  path="/path/to/audio/some.mp3"
  start = 1917117
  end = 1962282
  
  x, sr = librosa.load(path)
  start = round(start*sr/16000)
  end = round(end*sr/16000)
  sample = x[start: end]
  ipd.Audio(data=sample, rate=sr)

[Internal issue: 24]