owclassificationtree: Fix learner initialization
owclassificationtree: Fix learner initialization

Do not use split stopping parameters when disabled by the user.

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