Fix custom items

core/src/main/java/org/geysermc/geyser/registry/populator/ItemRegistryPopulator.java

@@ -379,6 +379,7 @@ public class ItemRegistryPopulator {
                         // ComponentItemData - used to register some custom properties
                         componentItemData.add(customMapping.componentItemData());
                         customItemOptions.add(Pair.of(customItem.customItemOptions(), customMapping.itemDefinition()));
+                        registry.put(customMapping.integerId(), customMapping.itemDefinition());
 
                         customIdMappings.put(customMapping.integerId(), customMapping.stringId());
                     }