Simplify document standalone setter (#15320)

The logic was very weird as it just should check whether the boolean is
true or not. And in fact the code is equivalent because zval_get_long()
will only return 0/1 because the type is a bool, and ZEND_NORMALIZE_BOOL
won't change that value.

Author: nielsdos

ext/dom/document.c

@@ -155,8 +155,8 @@ zend_result dom_document_standalone_write(dom_object *obj, zval *newval)
 {
 	DOM_PROP_NODE(xmlDocPtr, docp, obj);
 
-	zend_long standalone = zval_get_long(newval);
-	docp->standalone = ZEND_NORMALIZE_BOOL(standalone);
+	ZEND_ASSERT(Z_TYPE_P(newval) == IS_TRUE || Z_TYPE_P(newval) == IS_FALSE);
+	docp->standalone = Z_TYPE_P(newval) == IS_TRUE;
 
 	return SUCCESS;
 }