change velocity for RB3 pro guitar when it stays the same twice in a row (#18064)

There is a bug when you play twice in a row with the same velocity on a
string. The second note is not taken into account as the game does not
notice any change in the velocity.

It is because the velocity is never reset (or at least not very often).
The idea is to check if the velocity of the string is the same as the
previous one. And if it is, we just flip the last bit. Since the
accepted values goes from 6 to 127, from what I've seen, it should be
ok.

I don't have an official RB3 pro guitar, but I have a YouRock Guitar
that is compatible and works perfectly with a real MPA. When I use midi
in rpcs3, I miss notes because of that bug. I've add a log message to
test the patch and in a streak of nearly 150 notes, I should have missed
nearly 20 notes. I had absolutely no missed note with thanks to the
patch.

fixes https://github.com/RPCS3/rpcs3/issues/18062

---------

Co-authored-by: Romain Janvier <romain.janvier@ac-grenoble.fr>

rpcs3/Emu/Io/RB3MidiGuitar.cpp

@@ -265,7 +265,16 @@ void usb_device_rb3_midi_guitar::parse_midi_message(u8* msg, usz size)
 	// read strings
 	if (size == 8 && msg[0] == 0xF0 && msg[4] == 0x05)
 	{
-		button_state.string_velocities[msg[5] - 1] = msg[6];
+        // if the velocity remains the same, the game does not know that you've just played a string
+        u8& velocity = ::at32(button_state.string_velocities, msg[5] - 1);
+        if (msg[6] != 0 && msg[6] == velocity)
+        {
+		    velocity = msg[6] ^ 1;  // to be sure to change the velocity
+        }
+        else
+        {
+		    velocity = msg[6];
+        }
 	}
 
 	// read buttons