Fixes folder upload issue (#1877)

Adds missing variable declaration

Author: MarkGooding

js/fileinput.js

@@ -3048,6 +3048,7 @@
  },
  _addFilesFromSystem: function (e, dt, type) {
  var self = this,
+ i,
  files = dt.files,
  items = dt.items,
  folders = $h.getDragDropFolders(items);