Hanging notes at high arpeggiator speeds

[martinfinke]

The arpeggiator creates hanging notes at high speeds. In this line, if frequency is high, min_gate becomes > 1, and gate becomes > 1 as well. This can result in note_handler_->noteOff not getting called.

It seems that this can be fixed by limiting min_gate to be ≤ 1:

mopo_float min_gate = std::min((MIN_VOICE_TIME + VOICE_KILL_TIME) * frequency, 1.0);