fix: retrieve character entity within binding (#46)

In #45 the character entity was cached outside of the binding
evaluation. However, it in multiplayer games it can happen that it is
`null`, and therefore opening container screens on a connected client
fails.

This is fixed by retrieving the character entity with each binding
evaluation via a common helper method `getPredictedInteractionTarget`.

src/main/java/org/terasology/module/inventory/ui/ContainerScreen.java

@@ -14,6 +14,7 @@
 import org.terasology.nui.widgets.UILabel;
 
 /**
+ * A UI screen to show a container inventory next to the player's inventory.
  */
 public class ContainerScreen extends CoreScreenLayer {
 
@@ -23,8 +24,6 @@ public class ContainerScreen extends CoreScreenLayer {
     @In
     private TranslationSystem i18n;
 
-    private InventoryGrid containerInventory;
-
     @Override
     public void initialise() {
         InventoryGrid inventory = find("inventory", InventoryGrid.class);
@@ -37,19 +36,18 @@ public EntityRef get() {
         inventory.setCellOffset(10);
 
         UILabel containerTitle = find("containerTitle", UILabel.class);
-        containerInventory = find("container", InventoryGrid.class);
+        InventoryGrid containerInventory = find("container", InventoryGrid.class);
 
-        EntityRef characterEntity = localPlayer.getCharacterEntity();
         containerInventory.bindTargetEntity(new ReadOnlyBinding<EntityRef>() {
             @Override
             public EntityRef get() {
-                return characterEntity.getComponent(CharacterComponent.class).predictedInteractionTarget;
+                return getPredictedInteractionTarget();
             }
         });
         containerTitle.bindText(new ReadOnlyBinding<String>() {
             @Override
             public String get() {
-                Prefab parentPrefab = characterEntity.getComponent(CharacterComponent.class).predictedInteractionTarget.getParentPrefab();
+                Prefab parentPrefab = getPredictedInteractionTarget().getParentPrefab();
                 DisplayNameComponent displayName = parentPrefab.getComponent(DisplayNameComponent.class);
                 if (displayName != null) {
                     // The display name may contain a translatable string reference, thus we attempt to get the translation.
@@ -63,6 +61,14 @@ public String get() {
         });
     }
 
+    /**
+     * Retrieve the predicted interaction target entity for the local player.
+     */
+    private EntityRef getPredictedInteractionTarget() {
+        EntityRef characterEntity = localPlayer.getCharacterEntity();
+        return characterEntity.getComponent(CharacterComponent.class).predictedInteractionTarget;
+    }
+
     @Override
     public boolean isModal() {
         return false;