fix: [Up-port] Avoid throwing exception when using NetworkList without a NetworkManager#3503

EmandM wants to merge 4 commits intodevelop-2.0.0Unity-Technologies/com.unity.netcode.gameobjects:develop-2.0.0from

fix/2.x/network-manager-exceptionUnity-Technologies/com.unity.netcode.gameobjects:fix/2.x/network-manager-exceptionCopy head branch name to clipboard