Allow mulchmax to create regions of SV based on selected notes

The mulchmax feature is now more forgiving:

• If the selected region does not contain 2 or more SVs, it imagines 1x SVs on the start and end of the selected region.
• This now allows you to use mulch on its own to quickly create linear, exponentials, and other exciting SV effects without having to use other plugins to create the SV first.