fixed bug when plotting Bloch sphere with no data
fixed bug when plotting Bloch sphere with no data

anubhavvardhan/qutip,anubhavvardhan/qutip,qutip/qutip,qutip/qutip,cgranade/qutip,cgranade/qutip,zasdfgbnm/qutip,zasdfgbnm/qutip