[libxml2] parser: Fix potential memory leak in xmlParseAttValueInternal

[Nick Wellnhofer <nwellnhof src gnome org>]

commit 1a2d8ddc066143d256fdb8cc554707fe141dd2f6
Author: Nick Wellnhofer <wellnhofer aevum de>
Date:   Tue Oct 11 13:02:47 2022 +0200

    parser: Fix potential memory leak in xmlParseAttValueInternal
    
    Fix memory leak in case xmlParseAttValueInternal is called with a NULL
    `len` a non-NULL `alloc` argument. This static function is never called
    with such arguments internally, but the misleading code should be fixed
    nevertheless.
    
    Fixes #422.

 parser.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/parser.c b/parser.c
index 7bb47366..337e62f6 100644
--- a/parser.c
+++ b/parser.c
@@ -9155,6 +9155,7 @@ xmlParseAttValueInternal(xmlParserCtxtPtr ctxt, int *len, int *alloc,
     in++;
     col++;
     if (len != NULL) {
+        if (alloc) *alloc = 0;
         *len = last - start;
         ret = (xmlChar *) start;
     } else {
@@ -9164,7 +9165,6 @@ xmlParseAttValueInternal(xmlParserCtxtPtr ctxt, int *len, int *alloc,
     CUR_PTR = in;
     ctxt->input->line = line;
     ctxt->input->col = col;
-    if (alloc) *alloc = 0;
     return ret;
 need_complex:
     if (alloc) *alloc = 1;