Make torsions next to nitro groups consistent

[bannanc]

When typing emolecules, I came across this anomaly.

Only one torsion in this nitro group next two an N-N bond was missing which means we have a torsion for the [#8-1:1]-[#7+1:2]-[#7:3]-[#6:4] part, but not the double bonded part. SMIRNOFF shouldn't treat the two O~N bonds differently so we need to investigate why they're being treated asymmetrically.