fix(updater): handle null and non-object prefs in appUpdatesEnabled

[hsusul]

Fixes #1827

Problem

In src/helpers/updateCheckPolicy.js:
appUpdatesEnabled({ notificationsEnabled, notifyUpdates } = {}) threw TypeError: Cannot destructure property 'notificationsEnabled' of 'null' as it is null when passed null.

Solution

• Defaulted parameters safely to handle null and non-object values before destructuring.
• Added unit tests in test/helpers/updateCheckPolicy.test.js.

Verification

• node --test test/helpers/updateCheckPolicy.test.js (passes, 3/3 tests)
• npm run typecheck (passes, 0 errors)
• npm run lint (passes, 0 errors)
• npm run i18n:check (passes)
• npm run build:renderer (passes)
• git diff --check (clean)

[Chadpiha]

Thank you @hsusul — tidy PR and a thorough verification list, as always.

Closing this along with #1827: both call sites (updater.js) pass windowManager?.notificationPrefs, which is initialized in the constructor to a complete object and only ever key-mutated behind an existing !prefs || typeof prefs !== "object" guard at the IPC boundary (sync-notification-preferences) — so null can't reach the helper. The undefined case (missing windowManager via ?.) is already covered by the = {} default and pinned by an existing test.

There's also a behavioral reason we'd keep the throw: this helper enforces the #1605 contract ("only an explicit false disables update checks"). If pref state were ever corrupted to null, silently returning true would quietly re-enable update checks — for that invariant we'd rather crash loudly than fail open.

Appreciate you poking at the updater gating — thanks again!