fallback to default locate logic if no API found

patches/server/Add-StructuresLocateEvent.patch

@@ -85,6 +85,7 @@ index 0000000000000000000000000000000000000000..00000000000000000000000000000000
 +        final var paperRegistry = io.papermc.paper.registry.PaperRegistry.getRegistry(io.papermc.paper.registry.RegistryKey.CONFIGURED_STRUCTURE_REGISTRY);
 +        final List<io.papermc.paper.world.structure.ConfiguredStructure> configuredStructures = new ArrayList<>();
 +        paperRegistry.convertToApi(structures, configuredStructures::add, false); // gracefully handle missing api, use tests to check (or exclude)
++        if (!configuredStructures.isEmpty()) {
 +            final io.papermc.paper.event.world.StructuresLocateEvent event = new io.papermc.paper.event.world.StructuresLocateEvent(bukkitWorld, origin, configuredStructures, radius, skipReferencedStructures);
 +            if (!event.callEvent()) {
 +                return null;
@@ -96,6 +97,7 @@ index 0000000000000000000000000000000000000000..00000000000000000000000000000000
 +            radius = event.getRadius();
 +            skipReferencedStructures = event.shouldFindUnexplored();
 +            structures = HolderSet.direct(paperRegistry::getMinecraftHolder, event.getConfiguredStructures());
++        }
 +        // Paper end
          Map<StructurePlacement, Set<Holder<Structure>>> map = new Object2ObjectArrayMap();
          Iterator iterator = structures.iterator();