fix(notifications): Handle null provider in organization integrations filter

The organization integrations filter crashes when an entry has a null
provider, causing the notification settings page to error. Add optional
chaining to match the pattern already used for identity filtering.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: mtopo27

static/app/views/settings/account/notifications/notificationSettingsByType.tsx

@@ -103,7 +103,7 @@ export function NotificationSettingsByType({notificationType}: Props) {
       {staleTime: 30_000}
     );
   const organizationIntegrations = allOrgIntegrations.filter(orgIntegration =>
-    ALLOWED_PROVIDERS.has(orgIntegration.provider.key as SupportedProviders)
+    ALLOWED_PROVIDERS.has(orgIntegration?.provider?.key as SupportedProviders)
   );
   const {data: defaultSettings, status: defaultSettingsStatus} =
     useApiQuery<DefaultSettings>([getApiUrl('/notification-defaults/')], {