Fix a bug in our bug 9776 fix.

By calling circuit_n_chan_done() unconditionally on close, we were
closing pending connections that might not have been pending quite for
the connection we were closing.  Fix for bug 9880.

Thanks to skruffy for finding this and explaining it patiently until
we understood.
Merge branch 'bug9880_fix' into maint-0.2.4