Cancelling the edition of a site doesn't restore the original values

[ggiraldez]

How to reproduce:

1. Open a collection
2. Go to a site
3. Edit the site
4. Clear the name field
5. Click on "Cancel"

Actual results: the site name disappeared. Even when going back to the site list, the name is blank.

Expected: the site name is restored upon cancelling the edition.

[mmuller]

Reproducible in version 2.17.2

[mmuller]

Working properly in version da54b36