TMultiGraph Axis bins and Zoom

I found the issue and I will fix it in root trunk.
It is easy to bypass by adding a first graph. The problem shows up because you have only one graph.

   const UInt_t N=100000;
   Double_t x[N];
   Double_t y[N];
   for(int i=0;i<N;i++) {x[i]=i;y[i]=i+1;}
   TMultiGraph* mg = new TMultiGraph("mg","mg");
   TGraph* g1 = new TGraph(1); g1->SetPoint(0,0.,0.); mg->Add(g1);
   TGraph* gr = new TGraph(100000,x,y);
   cout<<mg->GetXaxis()->GetNbins()<< " "<< gr->GetXaxis()->GetNbins() <<endl;