MIDI - fixedInputVelocity applied to every event

MidiPort.cpp lines 131-148
The following code should be moved inside the test just above. FixedInputVelocity should only be applied to relevant events.
```
if( fixedInputVelocity() >= 0 && inEvent.velocity() > 0 )
{ inEvent.setVelocity( fixedInputVelocity() ); }
```

Start by inspecting MidiPort.cpp lines 131-148 and the test immediately above the shown code. Move the fixedInputVelocity condition into that test, then verify that fixed input velocity is applied only to relevant events and not every MIDI event.

Written by the indexing model from the issue text.