Value: Fix a wrong condition check in `Value.__hash__`.
Value: Fix a wrong condition check in `Value.__hash__`.

For values of continuous variables it would xor two same hashes
(always producing 0). Fix by checking the actual slot `_value`
and not the accessor `value`.

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