don't build preemptive conflux circuits if no predicted ports

Conflux circuit building was ignoring the "predicted ports" feature, which aims to make Tor stop building circuits if there have been no user requests lately. This bug led to every idle Tor on the network building and discarding circuits every 30 seconds, which added overall load to the network, used bandwidth and battery from clients that weren't actively using their Tor, and kept sockets open on guards which added connection padding essentially forever.

Bug went in on commit 39c2927d when we added preemptive conflux circuit pools.

Fixes bug 40981; bugfix on 0.4.8.1-alpha.

mentioned in merge request !837 (closed)

requested review from @dgoulet

changed milestone to %Tor: 0.4.8.x-post-stable

(This is an improved version of the previous merge request, !837 (closed), go there to see comments and past discussion)

approved this merge request

This looks good to me!

mentioned in issue #40981 (closed)

approved this merge request

merged manually

Wow, this is excellent catch and work!! Love it.

I just merged forward this manually.

assigned to @arma

Nice catch here

mentioned in issue #40893 (closed)