packagekit: ensure that the component is mounted before executing async callbacks
packagekit: ensure that the component is mounted before executing async callbacks

This fixes the error: Can't perform a React state update on an unmounted
component

This appears if we leave the updates page while it's loading.

cockpit-project/cockpit,cockpit-project/cockpit,martinpitt/cockpit,garrett/cockpit,garrett/cockpit,mvollmer/cockpit,garrett/cockpit,martinpitt/cockpit,garrett/cockpit,garrett/cockpit,martinpitt/cockpit,cockpit-project/cockpit,mvollmer/cockpit,cockpit-project/cockpit,mvollmer/cockpit,mvollmer/cockpit,martinpitt/cockpit,cockpit-project/cockpit,martinpitt/cockpit,mvollmer/cockpit