Fix velocity spike when releasing keys

* If >= 8 keys are pressed, there will be a max velocity spike when a key
  is released and the assigner attempts to reassign with the intent of
  finding a key that is presed but which no voices are playing, and
  assign it.
* The reason is that in the loop after the block in which restoredNote
  is set, if there is no voice corresponding to the key just released
  (such as when releasing #1 of an 8 key pressed; the voice corresponding
  to the #1 key will have been stolen so that there is no voice playing it),
  the loop attempting to gate off the voice or find an oldVel for the
  new allocation, will fall terminate without oldVel being set, which
  causes it to be set to UINT16_MAX.
When restoring note, set leagato also when not in mono mode
Cleanup in assigner_assignNote