MPE: Made the MPEInstrument::Listener methods virtual with empty implementations instead of pure virtual

modules/juce_audio_basics/mpe/juce_MPEInstrument.h

@@ -261,12 +261,12 @@ public:
         /** Implement this callback to be informed whenever a new expressive MIDI
             note is triggered.
         */
-        virtual void noteAdded (MPENote newNote) = 0;
+        virtual void noteAdded (MPENote newNote)                 { ignoreUnused (newNote); }
 
         /** Implement this callback to be informed whenever a currently playing
             MPE note's pressure value changes.
         */
-        virtual void notePressureChanged (MPENote changedNote) = 0;
+        virtual void notePressureChanged (MPENote changedNote)   { ignoreUnused (changedNote); }
 
         /** Implement this callback to be informed whenever a currently playing
             MPE note's pitchbend value changes.
@@ -275,12 +275,12 @@ public:
             master channel pitchbend event, or if both occur simultaneously.
             Call MPENote::getFrequencyInHertz to get the effective note frequency.
         */
-        virtual void notePitchbendChanged (MPENote changedNote) = 0;
+        virtual void notePitchbendChanged (MPENote changedNote)  { ignoreUnused (changedNote); }
 
         /** Implement this callback to be informed whenever a currently playing
             MPE note's timbre value changes.
         */
-        virtual void noteTimbreChanged (MPENote changedNote) = 0;
+        virtual void noteTimbreChanged (MPENote changedNote)     { ignoreUnused (changedNote); }
 
         /** Implement this callback to be informed whether a currently playing
             MPE note's key state (whether the key is down and/or the note is
@@ -289,14 +289,14 @@ public:
             Note: If the key state changes to MPENote::off, noteReleased is
             called instead.
         */
-        virtual void noteKeyStateChanged (MPENote changedNote) = 0;
+        virtual void noteKeyStateChanged (MPENote changedNote)   { ignoreUnused (changedNote); }
 
         /** Implement this callback to be informed whenever an MPE note
             is released (either by a note-off message, or by a sustain/sostenuto
             pedal release for a note that already received a note-off),
             and should therefore stop playing.
         */
-        virtual void noteReleased (MPENote finishedNote) = 0;
+        virtual void noteReleased (MPENote finishedNote)         { ignoreUnused (finishedNote); }
     };
 
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