core/transaction: fix cycle break attempts outside transaction

Patch fixes some incorrect-looking code in transaction.c.
It could fix cases where Debian users with bad package configurations
had systemd go into an infinite loop printing messages about breaking an
ordering cycle, though I have not reproduced that problem myself.

transaction_verify_order_one() considers jobs/units outside current
transaction when checking whether ordering dependencies cause cycles.
It would also incorrectly try to break cycles at these jobs; this
cannot work, as the break action is to remove the job from the
transaction, which is a no-op if the job isn't part of the transaction
to begin with. The unit_matters_to_anchor() test also looks like it
would not work correctly for non-transaction jobs. Add a check to
verify that the unit is part of the transaction before considering a
job a candidate for deletion.

https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=752259

src/core/transaction.c

@@ -381,7 +381,7 @@ static int transaction_verify_order_one(Transaction *tr, Job *j, Job *from, unsi
                                       "Found dependency on %s/%s",
                                       k->unit->id, job_type_to_string(k->type));
 
-                        if (!delete &&
+                        if (!delete && hashmap_get(tr->jobs, k->unit) &&
                             !unit_matters_to_anchor(k->unit, k)) {
                                 /* Ok, we can drop this one, so let's
                                  * do so. */