Accounts > Import > Preview: vote weight 0 isn't displayed and won't result in error message

[MSoeb]

Description: If an admin wants to import an account with vote weight 0 via a csv file, the preview doesn't show an error message. Only after import a correct error message appears.

preview doesn't include vote weight value 0 or warning

correct error message after file import:

Reproduction:

1. open Accounts > three-dot-menu > import
2. import a new user with vote weight zero -> check the preview

What should happen:
An error warning should appear in the preview before the data import. This would help the admin.
Possible solution: Warning sign at the line beginning. Also the vote weight value should be displayed and, if possible, a warning in the cell.

[luisa-beerboom]

Transferring this to the backend since the account import logic is handled there