user_test: panic on `rand.Read` error
user_test: panic on `rand.Read` error

Suggested by mlsteele.

Issue: #19007

keybase/client,keybase/client,keybase/client,keybase/client,keybase/client,keybase/client,keybase/client,keybase/client,keybase/client,keybase/client,keybase/client,keybase/client