[libxml2] fix memory leak in xmlAllocOutputBuffer

[Nick Wellnhofer <nwellnhof src gnome org>]

commit 4f67dbb0a1314326caac5e2780046c56210af2b1
Author: zhouzhongyuan <zhouzhongyuan huawei com>
Date:   Tue Jul 9 15:11:01 2019 +0800

    fix memory leak in xmlAllocOutputBuffer

 xmlIO.c | 1 +
 1 file changed, 1 insertion(+)
---
diff --git a/xmlIO.c b/xmlIO.c
old mode 100644
new mode 100755
index 299b6d21..3ab73398
--- a/xmlIO.c
+++ b/xmlIO.c
@@ -2383,6 +2383,7 @@ xmlAllocOutputBuffer(xmlCharEncodingHandlerPtr encoder) {
     if (encoder != NULL) {
         ret->conv = xmlBufCreateSize(4000);
        if (ret->conv == NULL) {
+            xmlBufFree(ret->buffer);
            xmlFree(ret);
            return(NULL);
        }