Fix not loading any plugins when pairing with MacOS
On macOS (and anywhere where the there's an MTU limit for UTP) those fields are not null but empty: https://invent.kde.org/network/kdeconnect-kde/-/blob/0640279ae0b60fcf6001e1e4735610e0ce71ffa2/core/backends/lan/lanlinkprovider.cpp#L238-239