[FIX] Black screen when try to open a chat with a non-existent department (#27609)

apps/meteor/app/livechat/imports/server/rest/departments.ts

apps/meteor/app/livechat/server/lib/Departments.ts

apps/meteor/app/livechat/server/lib/Livechat.js

apps/meteor/app/livechat/server/methods/removeDepartment.js

apps/meteor/app/models/server/models/LivechatDepartment.js

...teor/app/models/server/models/LivechatDepartmentAgents.js

...channel/directory/chats/contextualBar/DepartmentField.tsx

...nt/views/omnichannel/directory/hooks/useDepartmentInfo.ts

...livechat-enterprise/server/hooks/afterRemoveDepartment.js

...livechat-enterprise/server/hooks/afterRemoveDepartment.ts

.../meteor/ee/app/models/server/models/LivechatDepartment.js

apps/meteor/ee/server/models/LivechatDepartment.ts

apps/meteor/ee/server/models/raw/LivechatDepartment.ts

apps/meteor/ee/server/models/startup.ts

apps/meteor/lib/callbacks.ts

apps/meteor/packages/rocketchat-i18n/i18n/en.i18n.json

apps/meteor/server/models/raw/LivechatDepartment.ts

apps/meteor/server/models/raw/LivechatDepartmentAgents.ts

apps/meteor/server/models/raw/LivechatRooms.js

apps/meteor/tests/data/livechat/units.ts