[Notifications] Fall back to process ID when no desktop_entry is provided in Inhibit
xdg-desktop-portal forwards appId only for sandboxed apps it can trust, essentially blocking us from posting an inhibition from xdg-desktop-portal as we wouldn't have an app.
This enables xdg-desktop-portal-kde!33 (merged) to work for non-sandboxed apps like Firefox and Chrome under Wayland
Posted an inhibition from an app and passed an empty string:
