MPV: fix for nug IPAL13251

MPV: fix for nug IPAL13251
"Mandriva64 porting: SIGSEGV during partition"

myDS->Shape and myDS->GetShape methods is very dangerous to use in the equations like the next:

const TopoDS_Face& aFace = TopoDS::Faces(myDS->Shape(anIndex));

because this reference can be invalid after the next command execution:

myDS->InsertShapeAndAncestorsSuccessors(...)

This command some times deletes old shapes from internal array to make bigger array.