Fix NOTE OFF opcode with repeating macro

If an SSG note is stopped while its instrument contains a macro that
loops (e.g. arpeggio), the macro state is not reset, so the note is
not stopped.

To fix that, clear the EVAL_MACRO bit in addition to the PLAY bit.

nullsound: improve mute semantics when interacting with music API

- The sound keeps being muted when calling sound_stop
- The volume_up/down are now no-op

Initial release tag