Null Ref in StopHost/Client if StartHost/Client failed before

[jonasd683]

Describe the bug
Calling the StopHost method (internally StopClient) results in a NullReferenceException (NetworkServer.localConnection is null) if it is called after the StartHost has previously failed.

In other words: It is not possible to reset the mode to offline if server or client creation fails (e.g. if the socket address, protocol, network address or connection is already in use (System.Net.Sockets.SocketException).

[IMPORTANT] How can we reproduce the issue, step by step:

1. Start as Host with instance A.
2. Start a second Host with instance B.
3. An exception (System.Net.Sockets.SocketException, code 0x80004005) will occur on instance B, which is correct.
4. The NetworkManager.singleton.mode of instance B is still host.
5. Call StopHost on instance B to set the mode to offline.
6. A NullReferenceException will occur because the NetworkServer.localConnection is null in the StopClient method that is called internally. This should be caught.
7. The mode on instance B remains Host instead of offline.

Expected behavior
After calling StopHost/Client, the NetworkManager.singleton.mode should be offline. Even if an exception occurs when calling.

Is there any other way to reset the mode to offline?

Desktop (please complete the following information):

• OS: Windows
• Build target: all
• Unity version: 2022.3.62f1
• Mirror branch: 96.0.1 from Unity Asset Store