QVector3D::normalized fails (returns the zero vector) for very-short vectors

QVector3D::normalized tests length-squared; if it's "too short" it returns the zero vector. The problem is, "too short" isn't anywhere near where we'd have precision loss. For example, the vector

has a well-defined direction, but normalized will return zero.

I can see having a cutoff when length-squared approaches float32's minimum positive value (~1e-38) so when components have a length on the order of 1e-19, but the threshold now is closer to float epsilon (the smallest number you can add to 1.0f and get a result that's not 1.0f).

The same is true of the other QVectorND classes and QQuaternion.