Fix SimpleXML empty element boolean cast

Use the existing SimpleXML emptiness check for boolean casts instead of returning true for any existing node. This makes empty elements without attributes cast to false while keeping elements with text, attributes, or children truthy.

Author: prateekbhujel

ext/simplexml/simplexml.c

@@ -1839,12 +1839,7 @@ static zend_result sxe_object_cast_ex(zend_object *readobj, zval *writeobj, int
 	sxe = php_sxe_fetch_object(readobj);
 
 	if (type == _IS_BOOL) {
-		node = php_sxe_get_first_node_non_destructive(sxe, NULL);
-		if (node) {
-			ZVAL_TRUE(writeobj);
-		} else {
-			ZVAL_BOOL(writeobj, !sxe_prop_is_empty(readobj));
-		}
+		ZVAL_BOOL(writeobj, !sxe_prop_is_empty(readobj));
 		return SUCCESS;
 	}
 

ext/simplexml/tests/000.phpt

@@ -221,7 +221,7 @@ object(SimpleXMLElement)#%d (1) {
 }
 ===sxe->elem11->elem111->elem1111
 bool(true)
-bool(true)
+bool(false)
 int(1)
 object(SimpleXMLElement)#%d (0) {
 }

ext/simplexml/tests/gh21583.phpt

@@ -0,0 +1,31 @@
+--TEST--
+GH-21583 (empty SimpleXML child element casts to false)
+--EXTENSIONS--
+simplexml
+--FILE--
+<?php
+
+$xml = simplexml_load_string(<<<XML
+<root>
+    <empty/>
+    <with-text>content</with-text>
+    <with-attribute value="1"/>
+    <with-child><child/></with-child>
+</root>
+XML);
+
+var_dump((bool) $xml->empty);
+var_dump((bool) $xml->missing);
+var_dump((bool) $xml->{"with-text"});
+var_dump((bool) $xml->{"with-attribute"});
+var_dump((bool) $xml->{"with-child"});
+var_dump((bool) simplexml_load_string('<root/>'));
+
+?>
+--EXPECT--
+bool(false)
+bool(false)
+bool(true)
+bool(true)
+bool(true)
+bool(false)