Record listening - unsolicited message error when all clients unsubscribe

[jdmnd]

When providing a record using ds.record.listen(), if:

1. a remote client subscribes to the record, triggering a subscribe on the provider and

2. the provider subscribes to the record locally and

3. the remote client unsubscribes

then:

1. the provider's record subscription triggers a resubscribe on the listen callback and

2. the provider receives the error message: Error: UNSOLICITED_MESSAGE: foo/bar (R)

3. No error is logged on the server

What should happen:

The provider's record subscription is ignored.

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This issue first occurred in master in commit e7eea7c
and affects releases: v2.1.0, v2.1.1, v2.1.2

The referenced commit includes a fix for issue #476