fix/prevent trimming stream after removed

[stanley2058]

There's a possibility that the stream would be deleted before xTrim is called. When persisting in worker, a promise is created and would resolve once the worker is done processing persisting.

Where this line would be called:

y-socketio-redis/src/y-socket-io/y-socket-io.js

Line 680 in e85b438

this.client?.trimRoomStream(namespace, 'index', true)

Before this line:

y-socketio-redis/src/y-socket-io/y-socket-io.js

Line 539 in e85b438

await this.client.trimRoomStream(namespace, 'index')

Due to here also waiting on the same promise:

y-socketio-redis/src/y-socket-io/y-socket-io.js

Line 659 in e85b438

if (awaitingPersist) await awaitingPersist.promise

In this PR, we check if the namespace still exists before calling on the trim function. The namespace is deleted here:

y-socketio-redis/src/y-socket-io/y-socket-io.js

Line 678 in e85b438

this.namespaceDocMap.delete(namespace)

Just before deleting the stream, so we can assume the stream still exists in Redis if the namespace is still alive.