updated tidyup function for bug with zero matrices or matrices almost zero
updated tidyup function for bug with zero matrices or matrices almost zero

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