Fix play verification when a seek is queued.
Make LateNight-Stacked to use start_play.

Previously when play verification occurred, it would fail
if the play position was at the end of the track.  But if
a seek has been queued, that should still be allowed.  This was
causing the start_play button to fail every time the
sampler had been allowed to play the whole sample.
When clearing scale, allowing choosing crossfade or not
Fix if statement
Helpful comment
Right click should be start_stop
Right click should be start_stop, fix tooltip
Don't need EmitOnPress or ConnectValue any more
fix the actual bug, which is that reading past the end is ok.
Debug assert if math_clamp is used incorrectly
Merge branch 'master' into start_play_fix
Warn, don't crash, if math_clamp is used badly
Merge branch 'master' into start_play_fix
notify seek was in the right place, leave it there.
Merge pull request #282 from ywwg/start_play_fix

Fix bad use of math_clamp