BUG/MEDIUM: cli/proxy: don't try to dump idle connection state if there's none

Commit 69f591e3b ("MINOR: cli/proxy: add a new "show servers conn" command")
added the ability to dump the idle connections state for a server, but we
must not do this if idle connections were not allocated, which happens if
the server is configured with pool-max-conn 0.

This is 2.2, no backport is needed.
1 file changed