title: cxgrid footer format - sum time in HH:MM format
body: <p>In cxgrid,I am summing time in a footer (the field in question is a Time field).
  I have changed its property to TimeEdit and changed  its time display
  format to  'tfHourMin'. However I can not do that to the underlying footer.
  It keeps displaying hh:mm:ss. Is there a way to have the footer display also  'tfHourMin' format ???</p>
  
  <p>edit : If I do this I get "Could not convert variant of type (Null) into type (Double" error</p>
  
  <pre><code>procedure TForm1.cxGrid1DBTableView1TcxGridDBDataControllerTcxDataSummaryFooterSummaryItems1GetText(
    Sender: TcxDataSummaryItem; const AValue: Variant; AIsFooter: Boolean;
    var AText: string);
  begin
   AText := FormatDateTime('hh:mm', AValue);
  end;
  </code></pre>