Calculated question back to quiz button

Controlling the display of the Back to quiz editing button

The question\type\datasetdependent\datasetitems.php which code the display of the third and last form of the creation of a calculated question have been modified so that when there is no data the Back to quiz editing button does not appears items but instead there is a warning. When there is at least one set of data items, the Back to quiz editing button appears.