MessagingTemplate disconnect method should be idempotent

[abbiemery]

The disconnect method for the messaging errors if called when it is already disconnected. Instead it should do nothing. To avoid this causing issues the stop method in service handler has had a if statement added to it to check if its connected before trying to disconnect it, but this should be able to be taken back out.

[stan-dot]

what are the steps to reproduce the issue? which disconnect method is this?