Error characteristics curve throws exception in crossvalidation

[abeham]

I am testing CV in the async branch, but this also happens in the stable branch. To reproduce:

1. Create a new GA (I set MaximumGenerations to 20)
2. Set a new sym reg problem
3. Create a new CV and drag the GA to it (I used 5 folds)
4. Run the CV and view the "Best training solution (ensemble)"
5. Click on Error Characteristics Curve

The following exception is thrown

System.InvalidOperationException: Sequence contains no elements
   at System.Linq.Enumerable.Max(IEnumerable`1 source)
   at HeuristicLab.Problems.DataAnalysis.Views.RegressionSolutionErrorCharacteristicsCurveView.AddSeries(IRegressionSolution solution) in c:\Users\P40311\Work\core\stable\HeuristicLab.Problems.DataAnalysis.Views\3.4\Regression\RegressionSolutionErrorCharacteristicsCurveView.cs:line 167
   at HeuristicLab.Problems.DataAnalysis.Views.RegressionSolutionErrorCharacteristicsCurveView.UpdateChart() in c:\Users\P40311\Work\core\stable\HeuristicLab.Problems.DataAnalysis.Views\3.4\Regression\RegressionSolutionErrorCharacteristicsCurveView.cs:line 152
   at HeuristicLab.MainForm.WindowsForms.ContentView.set_Content(IContent value) in c:\Users\P40311\Work\core\stable\HeuristicLab.MainForm.WindowsForms\3.3\Views\ContentView.cs:line 52
   at HeuristicLab.MainForm.WindowsForms.ViewHost.OnContentChanged() in c:\Users\P40311\Work\core\stable\HeuristicLab.MainForm.WindowsForms\3.3\Controls\ViewHost.cs:line 150
   at HeuristicLab.MainForm.WindowsForms.ContentView.set_Content(IContent value) in c:\Users\P40311\Work\core\stable\HeuristicLab.MainForm.WindowsForms\3.3\Views\ContentView.cs:line 52
   at System.Windows.Forms.ListView.OnSelectedIndexChanged(EventArgs e)
   at System.Windows.Forms.ListView.WmReflectNotify(Message& m)
   at System.Windows.Forms.ListView.WndProc(Message& m)
   at System.Windows.Forms.NativeWindow.Callback(IntPtr hWnd, Int32 msg, IntPtr wparam, IntPtr lparam)

The error characteristics curve of each fold can be viewed separately without error.