Fix two race conditions (and possibly go routine leaks) in commands

[Stebalien]

fixes #4405

[keks]

Looks good, thanks!

[keks]

Huh, I did not know you could define types in functions. Neat!

[Stebalien]

You want to have some real fun?

ch := make(chan struct{pins []*cid.Cid, err error}, 1)
//...
ch <- struct{pins []*cid.Cid, err error}{err: errors.New("😎")}

[Kubuxu]

I have some other trick for you:

type System struct {
    cntrSafe struct {
        sync.Mutex
        n int
    }
    mapSafe struct {
        sync.Mutex
        m map[int]int
    }
}

usage

s := &System{}
s.cntrSafe.Lock()
s.cntrSafe.n++
s.cntrSafe.Unlock()