Data Exchange, Vrml - Recompute normals when the normal count is different to vertex count

Some VRML models define IndexedFaceSet with Normal as empty vector array.
This causes a "zero norm" exception in gp_Dir constructor when calling aTriangulation->SetNormal() in VrmlData_IndexedFaceSet::TShape.

Example structure:

Shape {
  appearance 
  Appearance {
    ...
  }
  geometry 
  IndexedFaceSet {
    coord 
    Coordinate {
      ...
    }
    normal 
    Normal {
      vector [  ]

    }
    coordIndex [
      ... ]
    ...
  }

},

Example file and patch are attached.

It is ok to push the patch without CLA.