observe code segfaults if sweeps that save do not end at corner

[g1257]

This should not be a problem because all previous data must have already being processed and printed by observe.
Some have noticed, however, that because the printing is probably buffered, sometimes the segfault precludes the printing from happening at all, particularly when running observe in a batch job.
WORKAROUND: Have the sweeps that save() to disk end at one of the corners.
() Sweeps that save are those that have the first bit of the 3rd number of the finite loop triplet set.