Cadnano Conversion fails on some configurations that have scaffold unbound to staples.

[joseph-schaeffer]

Reported by David Ruiz.

Cadnano 2.5 screenshot of offending scaffold area:

I thought we had a check for this, but the configuration here is slightly different than our test; @ktbolt is looking into a fix.

[joseph-schaeffer]

Resolved by #11.