Add a missing null check in simplexml

Author: nikic

ext/simplexml/simplexml.c

@@ -1390,6 +1390,11 @@ SXE_METHOD(registerXPathNamespace)
 	}
 
 	sxe = Z_SXEOBJ_P(ZEND_THIS);
+	if (!sxe->document) {
+		zend_throw_error(NULL, "SimpleXMLElement is not properly initialized");
+		RETURN_THROWS();
+	}
+
 	if (!sxe->xpath) {
 		sxe->xpath = xmlXPathNewContext((xmlDocPtr) sxe->document->ptr);
 	}

ext/simplexml/tests/simplexml_uninitialized.phpt

@@ -35,6 +35,11 @@ try {
 } catch (Error $e) {
     echo $e->getMessage(), "\n";
 }
+try {
+    var_dump($sxe->registerXPathNamespace('', ''));
+} catch (Error $e) {
+    echo $e->getMessage(), "\n";
+}
 try {
     var_dump($sxe->foo);
 } catch (Error $e) {
@@ -49,3 +54,4 @@ SimpleXMLElement is not properly initialized
 SimpleXMLElement is not properly initialized
 SimpleXMLElement is not properly initialized
 SimpleXMLElement is not properly initialized
+SimpleXMLElement is not properly initialized