Issues with enabling loop-points while playing and outside of the loop.

There is a bit of a glitch when you:
a. toggle loop-points to enabled, while...
b. we're already playing, and...
c. we're outside of the loop.

We will skip to tick 0 of the loop but will only play from the next tick, 1, for the first loop cycle. This doesn't happen when you toggle loop-points when playback is stopped. Also, notes playing aren't stopped which would probably be a good idea.

Start by reproducing the issue in LMMS with playback running outside the loop, then enable loop-points and observe the first loop cycle. Compare this with enabling loop-points while playback is stopped. Done means playback begins at tick 0 as expected and currently playing notes are stopped when loop-points are enabled.

Written by the indexing model from the issue text.