run: when waiting for unit, also check if no job is pending anymore

run: when waiting for unit, also check if no job is pending anymore

This is a fix-up for a7c71d214c37797d82de2f66cfe0a0a79c3a5c92: since we
now don't wait for the job to finish anymore right after enqueuing it,
we should not exit our ptyfwd logic before the unit is back to inactive
*and* no job pending anymore.