Fix clicks at loop-out when looping into lead-in

[daschuer]

This fixes a regression from f0870ff

[ronso0]

Can you please provide steps to reproduce/check the fix?

Here's a commit with a comment, and another small tweak
7570cda

[daschuer]

Here is the receipt to reproduce.

• Use a monotone test track like a 440 Hz sine tone.
• Create a loop starting at lead in
  -> hear the click sound at loop out. You may also record it and look at it using audacity

With this PR applied the click is smoothed out.

[ronso0]

I don't hear the clicks tbh, but I see the fading to zero.
LGTM, thanks!