OWTable: fix 'color by class' for continuous class_var
OWTable: fix 'color by class' for continuous class_var

marinkaz/orange3,marinkaz/orange3,marinkaz/orange3,cheral/orange3,qPCR4vir/orange3,cheral/orange3,cheral/orange3,qPCR4vir/orange3,qPCR4vir/orange3,kwikadi/orange3,kwikadi/orange3,cheral/orange3,marinkaz/orange3,qPCR4vir/orange3,kwikadi/orange3,qPCR4vir/orange3,kwikadi/orange3,kwikadi/orange3,cheral/orange3,marinkaz/orange3,kwikadi/orange3,cheral/orange3,marinkaz/orange3,qPCR4vir/orange3