Potential race condition in key value index

[KyleMaas]

Probably ought to wrap this in a mutex. Index can be set, potentially multiple times if done concurrently, before the observable finished updating:

margaret/indexes/mkv/index.go

Lines 114 to 128 in 22ed48a

	err = idx.db.Set([]byte(addr), raw)
	if err != nil {
	return fmt.Errorf("error in store:%w", err)
	}
	idx.l.Lock()
	defer idx.l.Unlock()
	obv, ok := idx.obvs[addr]
	if ok {
	err = obv.Set(v)
	if err != nil {
	return fmt.Errorf("error setting value in observable:%w", err)
	}
	}