deposit: ckeditor sanity check

* Avoid error if deposit form is not using ckeditor in any field.

Signed-off-by: Javier Martin Montull <javier.martin.montull@cern.ch>
fyi, this for loop can be written using `$.each`:
```javascript
$.each(CKEDITOR.instances, function(instance, editor) {
    $("#" + instance).val(editor.getData())
})
```