Query: /api/v1/stores panics when store is healthy - v0.14.0-rc.0

[cuotos]

Thanos v0.14.0-rc.0

When query is connected to a healthy Store, viewing /stores shows

accessing /api/v1/stores causes a panic.

Issue was introduced in #2809.

When nil error is passed to updateStoreStatus(store *storeRef, err error) results in a nil pointer here
status.LastError = &stringError{originalErr: err}

I've got a PR that i've tried to unit tests the entire function so should catch this.

I do not know all the details of how this worked before, I can only assume that *MOST of the errors that get passed to this will have custom Marshal methods, and this fix was to catch those errors that do not, as these will normally Marshal to {}.

Let me know if I've mis understood this.