Do not output sixel if driver does not support it

Allow overriding driver sixel support in Images scenario

Terminal.Gui/ConsoleDrivers/NetDriver.cs

@@ -1024,12 +1024,15 @@ internal class NetDriver : ConsoleDriver
                 Console.Write (output);
             }
 
-            foreach (var s in Application.Sixel)
+            if (ConsoleDriver.SupportsSixel)
             {
-                if (!string.IsNullOrWhiteSpace (s.SixelData))
+                foreach (var s in Application.Sixel)
                 {
-                    SetCursorPosition (s.ScreenPosition.X, s.ScreenPosition.Y);
-                    Console.Write (s.SixelData);
+                    if (!string.IsNullOrWhiteSpace (s.SixelData))
+                    {
+                        SetCursorPosition (s.ScreenPosition.X, s.ScreenPosition.Y);
+                        Console.Write (s.SixelData);
+                    }
                 }
             }
         }

Terminal.Gui/ConsoleDrivers/WindowsDriver.cs

@@ -127,11 +127,14 @@ internal class WindowsConsole
 
             _lastWrite = s;
 
-            foreach (var sixel in Application.Sixel)
+            if (ConsoleDriver.SupportsSixel)
             {
-                SetCursorPosition (new Coord ((short)sixel.ScreenPosition.X, (short)sixel.ScreenPosition.Y));
-                WriteConsole (_screenBuffer, sixel.SixelData, (uint)sixel.SixelData.Length, out uint _, nint.Zero);
+                foreach (var sixel in Application.Sixel)
+                {
+                    SetCursorPosition (new Coord ((short)sixel.ScreenPosition.X, (short)sixel.ScreenPosition.Y));
+                    WriteConsole (_screenBuffer, sixel.SixelData, (uint)sixel.SixelData.Length, out uint _, nint.Zero);
 
+                }
             }
         }
 

UICatalog/Scenarios/Images.cs

@@ -62,10 +62,13 @@ public class Images : Scenario
             Y = 1,
             CheckedState = ConsoleDriver.SupportsSixel
                 ? CheckState.Checked : CheckState.UnChecked,
-            CanFocus = false,
-            Enabled = false,
             Text = "Supports Sixel"
         };
+
+        cbSupportsSixel.CheckedStateChanging += (s, e) =>
+                                                {
+                                                    ConsoleDriver.SupportsSixel = e.NewValue == CheckState.Checked;
+                                                };
         _win.Add (cbSupportsSixel);
 
         var cbUseTrueColor = new CheckBox