ipn/localapi: treat ACME "invalid" state as terminal, log more

Fixes #3975

Change-Id: Idb2cc8d4730e140939898c7dcc15c2014acca142
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
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Internal Server Error - Gitea: Git with a cup of tea
500 Internal Server Error

Gitea Version: 1.28.0+dev-477-g8b6ad49a5f