Fix the drag-down autofill for 'vocabulary' cells in the Spreadsheet Editor

When using the drag-down autofill on a cell with a vocabulary widget for which you just set the value, the "copied" cells show the vocabulary entry's ID instead of the vocabulary entry's label.

How to reproduce:

• log in the Web UI
• create a Workspace and 2 Files in it
• go to the Workspace listing and hide all the columns except Title and Nature
• open the spreadsheet editor
• set the Nature cell of the first file to Accomodation application form (see how the directory entry label is rendered)
• use the drag-down autofill on the Nature cell of the first file to set the Nature cell of the second file

Expected result: the Nature cell of the second file is rendered with directory entry label Accomodation application form.
Actual result: the Nature cell of the second file is rendered with directory entry ID AccomodationApplicationForm.

This behavior does not happen when the value of the cell is already set to a value when opening the spreadsheet editor.
When the value of the cell is empty, then set, then drag-down autofill'ed, it misbehaves.