Fix and improve test case

We fix the erroneous doctype declaration, clarify the expectation, and
add a comment to clarify the purpose of the tag mismatch in the XML.

Author: cmb69

ext/xml/tests/bug71592.phpt

@@ -6,9 +6,11 @@ if (!extension_loaded('xml')) die('skip xml extension not available');
 ?>
 --FILE--
 <?php
+// The tag mismatch at the end of the XML is on purpose, to make sure that the
+// parser actually stops after the handler returns FALSE.
 $xml = <<<XML
 <?xml version="1.0" encoding="UTF-8"?>
-<!DOCTYPE p [
+<!DOCTYPE root [
   <!ENTITY pic PUBLIC "image.gif" "http://example.org/image.gif">
 ]>
 <root>
@@ -22,9 +24,9 @@ xml_set_external_entity_ref_handler($parser, function () {
     return false;
 });
 xml_parse($parser, $xml);
-var_dump(xml_get_error_code($parser));
+var_dump(xml_get_error_code($parser) === XML_ERROR_EXTERNAL_ENTITY_HANDLING);
 ?>
 ===DONE===
 --EXPECT--
-int(21)
+bool(true)
 ===DONE===