Silent disconnect when a handler throws

[xPaw]

SteamKit/SteamKit2/SteamKit2/Steam/SteamClient/SteamClient.cs

Lines 384 to 385 in 58562fc

	LogDebug( "SteamClient", "Unhandled '{0}' exception from '{1}' handler: '{2}'", ex.GetType().Name, key.Name, ex.Message );
	Disconnect();

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.