[libxml2] Fix memory leak in libxml_C14NDocSaveTo

[Nick Wellnhofer <nwellnhof src gnome org>]

commit 9a9dd31ba60bdf4d15c7739958551c05b6d754cb
Author: David King <amigadave amigadave com>
Date:   Wed Jul 14 15:28:56 2021 +0100

    Fix memory leak in libxml_C14NDocSaveTo
    
    Found by Coverity.
    
    https://bugzilla.redhat.com/show_bug.cgi?id=1938806

 python/libxml.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)
---
diff --git a/python/libxml.c b/python/libxml.c
index 9196b620..e6a9e9f3 100644
--- a/python/libxml.c
+++ b/python/libxml.c
@@ -3725,7 +3725,10 @@ libxml_C14NDocSaveTo(ATTRIBUTE_UNUSED PyObject * self,
     buf = xmlOutputBufferCreateFile(output, NULL);
 
     result = PyxmlNodeSet_Convert(pyobj_nodes, &nodes);
-    if (result < 0) return NULL;
+    if (result < 0) {
+        xmlOutputBufferClose(buf);
+        return NULL;
+    }
 
     if (exclusive) {
         result = PystringSet_Convert(pyobj_prefixes, &prefixes);
@@ -3734,6 +3737,7 @@ libxml_C14NDocSaveTo(ATTRIBUTE_UNUSED PyObject * self,
                 xmlFree(nodes->nodeTab);
                 xmlFree(nodes);
             }
+            xmlOutputBufferClose(buf);
             return NULL;
         }
     }