chassis: Fix calldown logic in device extensions

This fixes a bug where the layer chassis did not call down properly in
vkEnumerateDeviceExtensionProperties if pLayerName was null. This
prevented other layers from ever seeing the call.
diff --git a/scripts/layer_chassis_generator.py b/scripts/layer_chassis_generator.py
index b5ee1c4..babceb6 100644
--- a/scripts/layer_chassis_generator.py
+++ b/scripts/layer_chassis_generator.py
@@ -760,7 +760,7 @@
     if (pLayerName && !strcmp(pLayerName, global_layer.layerName)) return util_GetExtensionProperties(0, NULL, pCount, pProperties);
     assert(physicalDevice);
     auto layer_data = GetLayerDataPtr(get_dispatch_key(physicalDevice), layer_data_map);
-    return layer_data->instance_dispatch_table.EnumerateDeviceExtensionProperties(physicalDevice, NULL, pCount, pProperties);
+    return layer_data->instance_dispatch_table.EnumerateDeviceExtensionProperties(physicalDevice, pLayerName, pCount, pProperties);
 }
 
 VKAPI_ATTR VkResult VKAPI_CALL CreateInstance(const VkInstanceCreateInfo *pCreateInfo, const VkAllocationCallbacks *pAllocator,