privacybydesign/irmago: irmaclient/revocation.go; 17 LoC

Found a possible issue in [privacybydesign/irmago](https://www.github.com/privacybydesign/irmago) at [irmaclient/revocation.go](https://github.com/privacybydesign/irmago/blob/2691b66ca19a8b62b809ef300c36fbaa4ef8d2e8/irmaclient/revocation.go#L91-L107)

Below is the message reported by the analyzer for this snippet of code. Beware that the analyzer only reports the first issue it finds, so please do not limit your consideration to the contents of the below message.

> range-loop variable id used in defer or goroutine at line 102

[Click here to see the code in its original context.](https://github.com/privacybydesign/irmago/blob/2691b66ca19a8b62b809ef300c36fbaa4ef8d2e8/irmaclient/revocation.go#L91-L107)

Click here to show the 17 line(s) of Go which triggered the analyzer.

```go
for id := range request.Disclosure().Identifiers().CredentialTypes {
credtype := client.Configuration.CredentialTypes[id]
if !credtype.RevocationSupported() {
continue
}
if !base.RequestsRevocation(id) {
continue
}
irma.Logger.WithField("credtype", id).Debug("updating witnesses")
wg.Add(1)
go func() {
if e := client.nonrevUpdate(id, base.Revocation[id].Updates); e != nil {
err = e // overwrites err from previously finished call, if any
}
wg.Done()
}()
}

```

Leave a reaction on this issue to contribute to the project by classifying this instance as a **Bug** :-1:, **Mitigated** :+1:, or **Desirable Behavior** :rocket:
See the descriptions of the classifications [here](https://github.com/github-vet/rangeclosure-findings#how-can-i-help) for more information.

commit ID: 2691b66ca19a8b62b809ef300c36fbaa4ef8d2e8

Start in irmaclient/revocation.go at lines 91-107 and inspect the reported range-loop capture in the goroutine, along with the surrounding revocation update flow. Check the existing Go tests for this path; done means the analyzer warning is addressed without changing the intended concurrent updates, and the relevant tests pass.

Written by the indexing model from the issue text.