* Calculate loudness for short or silent selections as well.
In case of selections shorter than 400ms (one momentary loudness block),
take what we have got and divide only be the actual length.
Abort loudness normalization silently if the selected audio is all
silent.
* Fix loudness effect bug when selection includes a gap.
If the selected audio in a track contained a gap between two clips,
an incorrect amount of samples was processed.
Max Maisel
Paul Licameli
Max Maisel