Modification of proposed fix to bug #6503
Based on discussion on relax-devel at gna dot org: https://mail.gna.org/public/relax-devel/2006-08/msg00033.html
This modification does not raise RelaxError if the amide bond length is 0, but rather sets the bond vector to None
Authored by: macraild 2006-08-09
Parent: [r2530]
Child: [r2532]
