Exporting FOOTER in csv with customFunction behaviour is broken!!!

[AndraPanait]

BUG description:

• if you have a function added inside the footer of one column : and you have just a couple of visible columns defined, the export of the csv footer is broken, i ll paste the code and tell you what the problem is!
  inside exporter.js you have this code for footer:
  if (!ignoreFooter) {
  content += '\n';
  content += visibleColumns.map(function (m, i) {
  if (typeof m.footer === 'function') {
  var columnData = _.pluck(data, columns[i].dataField);
  return '"' + m.footer(columnData, columns[i], i) + '"';
  } else if (m.footerFormatter) {
  return '"' + m.footerFormatter(columns[i], i) + '"';
  }
  return '"' + m.footer + '"';
  }).join(separator);
  }

what happens if visibleColums length is 7 and columns 10 for example?
columns[i] will be completely broken so ...all the code inside this function should be based on visibleColumns not on columns