Ignore BoundItem#bind if already bound

This makes it possible to bind an item to a gui and then add it to another one. (e.g. tab buttons in a paged gui)

Author: NichtStudioCode

invui/src/main/java/xyz/xenondevs/invui/item/AbstractBoundItem.java

@@ -21,7 +21,7 @@ public Gui getGui() {
     @Override
     public void bind(Gui gui) {
         if (this.gui != null)
-            throw new IllegalStateException("Gui is already bound");
+            return;
 
         this.gui = gui;
     }

invui/src/main/java/xyz/xenondevs/invui/item/BoundItem.java

@@ -28,7 +28,6 @@ public sealed interface BoundItem extends Item permits AbstractBoundItem {
      * Called when the item is added to a {@link Gui}.
      *
      * @param gui The {@link Gui} to bind this item to.
-     * @throws IllegalStateException If this item is already bound to a {@link Gui}.
      */
     void bind(Gui gui);