Add required-entry

Author: crissanclick

app/code/Magento/Customer/etc/adminhtml/system.xml

@@ -199,7 +199,7 @@
                     <label>Number of Lines in a Street Address</label>
                     <backend_model>Magento\Customer\Model\Config\Backend\Address\Street</backend_model>
                     <comment>Valid range: 1-4</comment>
-                    <validate>validate-digits validate-digits-range digits-range-1-4</validate>
+                    <validate>required-entry validate-digits validate-digits-range digits-range-1-4</validate>
                 </field>
                 <field id="prefix_show" translate="label comment" type="select" sortOrder="20" showInDefault="1" showInWebsite="1" showInStore="0">
                     <label>Show Prefix</label>