Follow-up to close() refactoring in r1547553
Fix some edge cases identified in some soon to be committed refactoring.

git-svn-id: https://svn.apache.org/repos/asf/commons/proper/dbcp/trunk@1547582 13f79535-47bb-0310-9956-ffa450edef68
Simplify.
DelegatingConnection already calls its own checkOpen that performs the same test.
No need to keep a second reference to the inner connection.

git-svn-id: https://svn.apache.org/repos/asf/commons/proper/dbcp/trunk@1547583 13f79535-47bb-0310-9956-ffa450edef68