notifications/cancelled is ignored for request id 0

[felixweinberger]

Protocol._oncancel guards with a falsy check (protocol.ts:337):

if (\!notification.params.requestId) {
    return;
}

so a notifications/cancelled carrying requestId: 0 is treated like an absent id and the in-flight handler keeps running. Id 0 is a legal JSON-RPC request id — it's the id this SDK's own client assigns to initialize, since the per-instance counter is zero-based.

Fix is requestId \!== undefined (or \!= null) instead of truthiness.

[anneheartrecord]

I have a fix ready for this (one-line !== undefined guard in Protocol._oncancel plus a regression test with request id 0, and a changeset): https://github.com/anneheartrecord/typescript-sdk/tree/fix/2283-cancelled-requestid-zero — PR creation on this repo is currently restricted for first-time contributors, so I'll open the PR as soon as that allows. Same situation for #2284 (branch fix/2284-invalid-params-error-code).