[libxml2] Fix SEGV in xmlSAXParseFileWithData

[Nick Wellnhofer <nwellnhof src gnome org>]

commit 7929f05710134b9b243952019b6c14066cd3ac9e
Author: yanjinjq <jiqin ji huawei com>
Date:   Sun Aug 30 10:34:01 2020 +0000

    Fix SEGV in xmlSAXParseFileWithData
    
    Fixes #181.

 parser.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/parser.c b/parser.c
index be14c3228..f779eb6a1 100644
--- a/parser.c
+++ b/parser.c
@@ -14077,7 +14077,7 @@ xmlSAXParseFileWithData(xmlSAXHandlerPtr sax, const char *filename,
 
     if ((ctxt->wellFormed) || recovery) {
         ret = ctxt->myDoc;
-       if (ret != NULL) {
+       if ((ret != NULL) && (ctxt->input->buf != NULL)) {
            if (ctxt->input->buf->compressed > 0)
                ret->compression = 9;
            else