Don't crash when docutils error has no line number
Don't crash when docutils error has no line number

Fixes #920

JohnTroony/nikola,masayuko/nikola,x1101/nikola,gwax/nikola,okin/nikola,schettino72/nikola,atiro/nikola,berezovskyi/nikola,x1101/nikola,andredias/nikola,TyberiusPrime/nikola,techdragon/nikola,lucacerone/nikola,jjconti/nikola,gwax/nikola,pluser/nikola,s2hc-johan/nikola,xuhdev/nikola,JohnTroony/nikola,masayuko/nikola,berezovskyi/nikola,wcmckee/nikola,jjconti/nikola,okin/nikola,knowsuchagency/nikola,yamila-moreno/nikola,gwax/nikola,atiro/nikola,wcmckee/nikola,schettino72/nikola,atiro/nikola,pluser/nikola,getnikola/nikola,xuhdev/nikola,jjconti/nikola,andredias/nikola,immanetize/nikola,knowsuchagency/nikola,TyberiusPrime/nikola,x1101/nikola,JohnTroony/nikola,masayuko/nikola,techdragon/nikola,getnikola/nikola,andredias/nikola,pluser/nikola,yamila-moreno/nikola,techdragon/nikola,s2hc-johan/nikola,xuhdev/nikola,schettino72/nikola,xuhdev/nikola,s2hc-johan/nikola,lucacerone/nikola,okin/nikola,getnikola/nikola,wcmckee/nikola,getnikola/nikola,lucacerone/nikola,knowsuchagency/nikola,berezovskyi/nikola,yamila-moreno/nikola,TyberiusPrime/nikola,okin/nikola,immanetize/nikola,immanetize/nikola