Thanks for your file.
Unfortunately, nothing is recoverable from your file, because it contains only zeros. It's not the first time it happens, but I (and other experts I asked) have no idea how this can happen.
Check in the subfolders of C:\Users\user\AppData\Roaming\eTeks\Sweet Home 3D\work (where user is your login) if there are some files starting by open and ending with .sweethome3d. If such files exist, copy the most recent one, change its extension by .sh3d and try to open it with Sweet Home 3D.
By the way, did you encounter some program crash?