Bug #50547 Need to check and warn in not connection and not open

Description:
if i remove a connections that was previously in use in admin "server instances" this is not detected either at the time of removal or when server instance is opened.

Or if new with product I can create a server instance with no connection. This shouldn't "work"

How to repeat:
Open product with no connections and create server instance

Remove connection.

Suggested fix:
Don't start a server instance if not connection is defined. Just warn.
"Can't open the current server instance because it lacks a MySQL Connections.
Please create a connection if needed and then open manage server instances and select a connection.

Also warn if user closes w/o selecting a connection.

connection manager now informs that connections used in admin session cant be removed. fix will be included in 5.2.16

A 'change' entry has been added to the 5.2.16 changelog:

The Manage DB Connections dialog now prevents removal of a connection used by a server instance.