Silent disconnect when a handler throws

[xPaw]

https://github.com/SteamRE/SteamKit/blob/58562fcc6f6972181615a6d1ff98103b06f0e33f/SteamKit2/SteamKit2/Steam/SteamClient/SteamClient.cs#L384-L385

I couldn't figure out what was happening last time this happened because it silently logs the exception into the debug log (with no stacktrace) and just disconnects.

This time I had debug log enabled and got this:

18:01:12 [DEBUG] FreeLicense: Received free license: OK (5 apps: 375750, 1077600, 797410, 517630, 517630, 3 packages: 407024, 409937, 410395)
18:01:12 [STEAMKIT] SteamClient: Unhandled 'ArgumentException' exception from 'SteamApps' handler: 'An item with the same key has already been added. Key: 517630'

After that, SK2 started to constantly keep disconnecting with the same message (but without freelicense grant this time). Which eventually got me rate limited by the CM.

[xPaw]

Repro:

Steam.Instance.Apps.PICSGetAccessTokens(new System.Collections.Generic.List<uint>() { 440, 440 }, Enumerable.Empty<uint>());

EDIT: I created #787 to fix the exception in the handler.

However if a handler throws, it shouldn't just eat it into debuglog and silently disconnect. This needs to be improved.