In SetModel, check if histogram was actually created (coverititis).

git-svn-id: http://root.cern.ch/svn/root/trunk@43894 27541ba8-7e3a-0410-8455-c3a389f83636

graf3d/gl/src/TF2GL.cxx

@@ -58,6 +58,8 @@ Bool_t TF2GL::SetModel(TObject* obj, const Option_t* opt)
    fM = SetModelDynCast<TF2>(obj);
 
    fH = (TH2*) fM->CreateHistogram();
+   if (!fH) return kFALSE;
+
    fH->GetZaxis()->SetLimits(fH->GetMinimum(), fH->GetMaximum());
 
    if (dynamic_cast<TF3*>(fM))