Fix vertical piano mouse click unresponsiveness

`PianoRoll::mouseDoubleClickEvent` wasn't forwarding the event to the base class when not acting on the event. The base class calls `mousePressEvent`.

Fixes #3005

src/gui/editors/PianoRoll.cpp

@@ -1948,6 +1948,10 @@ void PianoRoll::mouseDoubleClickEvent(QMouseEvent * me )
 			enterValue( &nv );
 		}
 	}
+	else
+	{
+		QWidget::mouseDoubleClickEvent(me);
+	}
 }