lib3mf does not properly handle NaN

[martinweismann]

e.g.

adding a vertex

"Pos.m_Value[0] = 0.0; Pos.m_Value[1] = 1.0; Pos.m_Value[2] = NAN;

to a mesh does not throw an exception.

Neither does writing the model to file cause an error or warning.
Instead, the file will contain

Similar goes for reading 3MF files with NaN in them.

This needs to be changed.