'AddProvider' on LoggerFactory should throw ObjectDisposedException after being disposed

[artganify]

Simple scenario:

var loggerFactory = new LoggerFactory();
loggerFactory.Dispose();
loggerFactory.AddProvider(new LoggerProviderWithUnmanagedResources());
loggerFactory.Dispose();

The Dispose() on each ILoggerProvider is never being called a second time because the private member _disposed in LoggerFactory prevents a second call. An ObjectDisposedException is expected here.

Worth considering?