Fix javascript error with policy button (#10049)

Fix javascript console error when createRoot is called on a non-existant
element which is conditional.

Resolves #10043

Author: driusan

smarty/templates/main.tpl

@@ -74,15 +74,18 @@
               }
             });
 
-            headerPolicyRoot = ReactDOM.createRoot(
-                document.getElementById("header-policy-button")
-            );
-            headerPolicyRoot.render(
-                React.createElement(PolicyButton, {
-                    onClickPolicy: {$header_policy|json_encode},
-                    popUpPolicy: {$pop_up_policy|json_encode},
+            const policyButtonEl = document.getElementById("header-policy-button");
+            if (policyButtonEl) {
+                headerPolicyRoot = ReactDOM.createRoot(
+                    policyButtonEl
+                );
+                headerPolicyRoot.render(
+                    React.createElement(PolicyButton, {
+                        onClickPolicy: {$header_policy|json_encode},
+                        popUpPolicy: {$pop_up_policy|json_encode},
                 })
-            );
+                );
+            }
           });
         </script>
         <link type="text/css" href="{$baseurl}/css/jqueryslidemenu.css" rel="Stylesheet" />