Same person validating more than once causes more than one validation

[bhaugen]

From telegram:

Michalis K
Just bumped onto this bug...
Same person Validated 3 (!) times and the commitment appear as validated in Agents (and in Kispagi too)
https://agent.fair.coop/canvas/402/validate
Seems that sometimes (maybe when you click too fast? maybe a delay of some kind would help?) it is possible to validate more than once at the same time (it has happened to me several times)

Maybe can fix in the validation-saving code. If the same person has validated this event before, don't create another validation?

[fosterlynn]

This was probably happening a few days ago when the UI was not working properly, and people couldn't see when they had already validated.

We could add that check in the validation saving code, and that would be correct to have it on the server also, but I doubt it is worth it for a feature such as validation, since I am pretty sure the UI now covers it.