Fixed LeaveVoiceServer when Multiserver is disabled

src/Discord.Net/DiscordClient.cs

@@ -798,10 +798,18 @@ namespace Discord
 			CheckReady(); //checkVoice is done inside the voice client
 			if (serverId == null) throw new ArgumentNullException(nameof(serverId));
 
-			DiscordSimpleClient client;
-			if (_voiceClients.TryRemove(serverId, out client))
-				await client.Disconnect();
-		}
+			if (Config.EnableVoiceMultiserver)
+			{
+				DiscordSimpleClient client;
+				if (_voiceClients.TryRemove(serverId, out client))
+					await client.Disconnect();
+			}
+			else
+			{
+				_dataSocket.SendLeaveVoice(serverId);
+				await _voiceSocket.Disconnect();
+			}
+        }
 
 		private void SendInitialLog()
 		{

src/Discord.Net/DiscordSimpleClient.cs

@@ -248,10 +248,15 @@ namespace Discord
 
         protected virtual async Task Cleanup()
 		{
-			await _dataSocket.Disconnect().ConfigureAwait(false);
 			if (_enableVoice)
+			{
+				string voiceServerId = _voiceSocket.CurrentServerId;
+                if (voiceServerId != null)
+					_dataSocket.SendLeaveVoice(voiceServerId);
 				await _voiceSocket.Disconnect().ConfigureAwait(false);
-			
+			}
+			await _dataSocket.Disconnect().ConfigureAwait(false);
+
 			_currentUserId = null;
 			_gateway = null;
 			_token = null;