Add default value of supports_weights.
Add default value of supports_weights.

Fixes learners that do not support weights,
which crashed on data with weights.

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