When we don't have bridge descriptors, we try to build multihop circuits anyway.

Right now, when running with bridges (and the fix from !855 (merged)), our output has a bunch of warnings like this:

2022-11-15T15:18:55.536742Z  INFO tor_circmgr::mgr: Couldn't pick action for circuit attempt 1: Programming error
2022-11-15T15:18:55.536925Z  INFO tor_circmgr::mgr: Couldn't pick action for circuit attempt 1: Programming error
2022-11-15T15:18:55.537166Z  INFO tor_circmgr::mgr: Couldn't pick action for circuit attempt 1: Programming error
2022-11-15T15:18:55.537206Z  WARN tor_circmgr: Failed to build preemptive circuit [scrubbed]: Unable to find or build a circuit: Programming error
2022-11-15T15:18:55.537257Z  WARN tor_circmgr: Failed to build preemptive circuit [scrubbed]: Unable to find or build a circuit: Programming error
2022-11-15T15:18:55.537319Z  WARN tor_circmgr: Failed to build preemptive circuit [scrubbed]: Unable to find or build a circuit: Programming error

To me, this looks like we don't have a descriptor for our bridge, but we keep trying to build circuits anyway. We shouldn't do that.

This isn't our current blocking bug; it's just an annoyance. The real problem is that we can't parse this descriptor, which is #637 (closed).