BRepMesh_IncrementalMesh fail to discretize some zero-length free edges

conditions:
- enable Standard_ConstructionError exceptions in config
- set the BRepMesh_IncrementalMesh to use relative deflection
- try to mesh a shape with at least a zero-length free edge (for instance an edge with a 0-radius circle, as it can be found in the outer wire of a sphere)

Then a Standard_ConstructionError exception will be raised inside BRepMesh_IncrementalMesh::discretizeFreeEdges() > CPnts_TangentialDeflection::CPnts_TangentialDeflection() > GCPnts_TangentialDeflection::Initialize()

In my test, with a empty circle for instance, the computed deflection for this edge is less than Precision::Confusion(), which explains the exception.

one possible fix would be to modify BRepMesh_ShapeTool::RelativeEdgeDeflection to have a minimum value strictly greater than Precison::Confusion()