Magento2: change page layout if category has no products

You can do this job by a Plugin

Create di.xml file with the following content:
app/code/VendorName/Module_Name/etc/frontend/di.xml

<?xml version="1.0"?>
<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:ObjectManager/etc/config.xsd">
    <type name="Magento\Catalog\Controller\Category\View">
        <plugin name="no_product_category" type="VendorName\Module_Name\Plugin\Catalog\Controller\Category\View"/>
    </type> 
</config>

2. app/code/VendorName/Module_Name/Plugin/Catalog/Controller/Category/View.php

<?php
namespace VendorName\Module_Name\Plugin\Catalog\Controller\Category;

class View extends \Magento\Catalog\Controller\Category\View {

    public function afterExecute(\Magento\Catalog\Controller\Category\View $subject, $result) {
        $category = $this->_coreRegistry->registry('current_category');
        if(!$category->getProductCollection()->getSize()){
            $result->getConfig()->setPageLayout('1column');
        }
        return $result;
    }
}