Remove ObjectDisposedException as inner exception for connection timeout

[bgrainger]

Connection timeout is implemented by disposing a TcpClient; after this happens, the ObjectDisposedException is preserved as the InnerException for a MySqlException:

MySqlConnector/src/MySqlConnector/Core/ServerSession.cs

Line 1016 in 05abf00

throw new MySqlException(MySqlErrorCode.UnableToConnectToHost, "Connect Timeout expired.", ex);

This was done to provide additional diagnostic information.

Despite the clear outer exception message, this routinely gets reported as an ObjectDisposedException, e.g.,:

• Disposed socket on connect timeout #871
• System.ObjectDisposedException #881
• ObjectDisposedException: Cannot access a disposed object. Object name: 'System.Net.Sockets.Socket'. #548
• Cannot access a disposed object(Socket) leads to a Timeout expired MySqlException #1020

This may be exacerbated by monitoring tools reporting the inner exception. (This screenshot from Application Insights is a slightly different inner exception but I think I've seen the same problem with it.)

The ObjectDisposedException is really just a detail of how timeout is currently implemented and ultimately not germane to the connection timeout; to avoid potential confusion we should throw a MySqlException with no inner exception. (This is potentially a breaking change if anyone had a catch () when block based on the inner exception.)

[bgrainger]

Fixed in 1.3.13.