You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: ratingGUI.m
    path of file: ./repos/automagic/gui
    
    the code of the file until where you have to start completion: function varargout = ratingGUI(varargin)
% RATINGGUI MATLAB code for ratingGUI.fig
%      RATINGGUI is called by the mainGUI. A user must not call this gui 
%      directly. Hower
    
function channellistbox_Callback(hObject, eventdata, handles)
% hObject    handle to channellistbox (see GCBO)
% eventdata  reserved - to be defined in a future version of MATLAB
% handles    structure with handles and user data (see GUIDATA)
if( handles.project.current == -1)
    return;
end
project = handles.project;
index_selected = get(handles.channellistbox,'Value');

if( isempty(index_selected))
    return;
end