fix writing to framebuffer after console switch

Author: dlech

src/ConsoleApp.vala

@@ -68,6 +68,9 @@ namespace Ev3devKit {
             Object ();
             init ();
             Ui.Screen.active_screen = new Ui.Screen ();
+            notify["is-active"].connect ((s, p) => {
+                Ui.Screen.can_draw = is_active;
+            });
         }
 
         public override bool event (Grx.Event event) {

src/ui/Screen.vala

@@ -37,6 +37,11 @@ namespace Ev3devKit.Ui {
         Queue<uint?> key_queue;
         Context context;
 
+        /**
+         * Hack to prevent drawing during console switching.
+         */
+        internal static bool can_draw { get; set; default = true; }
+
         /**
          * Gets and sets the foreground color.
          *
@@ -254,7 +259,7 @@ namespace Ev3devKit.Ui {
          */
         protected bool draw () {
             handle_input ();
-            if (dirty) {
+            if (dirty && can_draw) {
                 set_current_context (context);
                 Window? top_window = null;
                 Window? top_dialog = null;