don't renumber if saving topology

Geo/GModelIO_MSH2.cpp

@@ -878,6 +878,12 @@ int GModel::_writeMSH2(const std::string &name, double version, bool binary,
                        int elementStartNum, int saveSinglePartition, bool multipleView,
                        bool renumberVertices)
 {
+  if(CTX::instance()->mesh.saveTopology){
+    if(renumberVertices)
+      Msg::Info("Disabling vertex renumbering (incompatible with saving topology)");
+    renumberVertices = false;
+  }
+
   FILE *fp;
   if(multipleView)
     fp = Fopen(name.c_str(), binary ? "ab" : "a");