Prevent DefaultContext from being unregistered from key event handlers

api/src/main/java/com/bartlomiejpluta/base/api/input/KeyEventHandler.java

@@ -3,4 +3,12 @@ package com.bartlomiejpluta.base.api.input;
 @FunctionalInterface
 public interface KeyEventHandler {
    void handleKeyEvent(KeyEvent event);
+
+   default void onKeyEventHandlerRegister() {
+      // do nothing
+   }
+
+   default void onKeyEventHandlerUnregister() {
+      // do nothing
+   }
 }

engine/src/main/java/com/bartlomiejpluta/base/engine/context/model/DefaultContext.java

@@ -16,6 +16,7 @@ import com.bartlomiejpluta.base.api.screen.Screen;
 import com.bartlomiejpluta.base.engine.audio.manager.SoundManager;
 import com.bartlomiejpluta.base.engine.core.engine.GameEngine;
 import com.bartlomiejpluta.base.engine.database.service.DatabaseService;
+import com.bartlomiejpluta.base.engine.error.AppException;
 import com.bartlomiejpluta.base.engine.gui.manager.FontManager;
 import com.bartlomiejpluta.base.engine.gui.manager.WidgetDefinitionManager;
 import com.bartlomiejpluta.base.engine.gui.render.NanoVGGUI;
@@ -249,6 +250,11 @@ public class DefaultContext implements Context, KeyEventHandler {
       }
    }
 
+   @Override
+   public void onKeyEventHandlerUnregister() {
+      throw new AppException("Context cannot be unregistered");
+   }
+
    @Override
    public void update(float dt) {
       gameRunner.update(dt);

engine/src/main/java/com/bartlomiejpluta/base/engine/ui/model/GLFWInput.java

@@ -54,10 +54,12 @@ public class GLFWInput implements Input {
    @Override
    public void addKeyEventHandler(@NonNull KeyEventHandler handler) {
       keyEventHandlers.addLast(handler);
+      handler.onKeyEventHandlerRegister();
    }
 
    @Override
    public void removeKeyEventHandler(@NonNull KeyEventHandler handler) {
       keyEventHandlers.remove(handler);
+      handler.onKeyEventHandlerUnregister();
    }
 }