Validate screen blank

[jonfroehlich]

This is probably because it's a new server with no data to validate but we should handle this more elegantly.

https://sidewalk-knox.cs.washington.edu/validate

Uncaught TypeError: Cannot read properties of undefined (reading 'labels_validated')
    at new Main (SVValidate.js:16:39)
    at validate:1127:24

[misaugstad]

Darn, looks like we just keep breaking this over and over! We fixed it for the 2nd (3rd?) time in #3394, but it looks like it's time for another round of fixing! Let's make sure that it's fixed on the new Validate Beta as well!