Changing engine on unsupported algorithm/problem configuration crashes HL

[epitzer]

When configuring an engine first with a valid problem, changing it later to an unsupported problem leaves the algorithm in "prepared" state which causes problems when changing the engine as the state of the new engine is not reflected in the GUI.

Steps (for example):

1. create new Tabu Search algorithm
2. set problem to new Traveling Salesman Problem
3. set problem to new Vehicle Routing Problem
4. change the engine
5. click on start

System.InvalidOperationException: Start not allowed in execution state "Stopped".
   at HeuristicLab.Core.Executable.Start() in c:\Users\P40031\workspace\hl3\trunk\sources\HeuristicLab.Core\3.3\Executable.cs:line 86
   at HeuristicLab.DebugEngine.DebugEngine.Start() in c:\Users\P40031\workspace\hl3\trunk\sources\HeuristicLab.DebugEngine\3.3\DebugEngine.cs:line 178
   at System.Windows.Forms.Button.OnMouseUp(MouseEventArgs mevent)
   at System.Windows.Forms.Control.WmMouseUp(Message& m, MouseButtons button, Int32 clicks)
   at System.Windows.Forms.Control.WndProc(Message& m)
   at System.Windows.Forms.ButtonBase.WndProc(Message& m)
   at System.Windows.Forms.Button.WndProc(Message& m)
   at System.Windows.Forms.NativeWindow.Callback(IntPtr hWnd, Int32 msg, IntPtr wparam, IntPtr lparam)