Disposing the server when RestartAfterListenError is true may result in a restarted socket

[mathieuvanloon]

We recently had an issue where shutting down the Fleck server (with Dispose()) did not succeed. In fact the socket restarted itself. It turned out to be caused by this code:

since RestartAfterListenError was true, when one of the open connection triggered an exception the server was automatically restarted. So for now we'll set RestartAfterListenError to false when shutting down.