Bug 5132: Close the tunnel if to-server conn closes after client (#957)

Bug 5132: Close the tunnel if to-server conn closes after client (#957)

Since commit 25d2603, blind CONNECT tunnel "jobs" (and equivalent) were
not destroyed upon a "lonely" to-server connection closure, leading to
memory leaks. And when a from-client connection was still present at the
time of the to-server connection closure, we did not try to reforward,
violating the spirit of commit 25d2603 changes. Calling retryOrBail() is
sufficient to handle both cases.