Small fixes on OpenTK support.

Quik.OpenTK/OpenTKPlatform.cs

@@ -37,6 +37,11 @@ namespace Quik.OpenTK
                 IsGLInitialized = true;
             }
 
+            window.Closing += (ea) =>
+            {
+                Environment.Exit(0);
+            };
+
             return port;
         }
 

Quik.OpenTK/OpenTKPort.cs

@@ -72,7 +72,8 @@ namespace Quik.OpenTK
             _vertexEngine.Reset();
             _vertexEngine.ProcessCommands(new QRectangle(), queue);
 
-            _window.Context.MakeCurrent();
+            if (!_window.Context.IsCurrent)
+                _window.Context.MakeCurrent();
 
             if (!_glDriver.IsInit)
                 _glDriver.Init();