[libxml2] Clear entity content in case of errors

[Nick Wellnhofer <nwellnhof src gnome org>]

commit 60dded12cbf1705927803c5ed615a7a0132aebbd
Author: Nick Wellnhofer <wellnhofer aevum de>
Date:   Mon Jan 22 15:04:58 2018 +0100

    Clear entity content in case of errors
    
    This only affects recovery mode and avoids integer overflow in
    xmlStringGetNodeList and possibly other nasty surprises.
    
    See bug 783052 and
    
    https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=3874
    https://bugs.chromium.org/p/chromium/issues/detail?id=796804

 parser.c |    4 +++-
 1 files changed, 3 insertions(+), 1 deletions(-)
---
diff --git a/parser.c b/parser.c
index afc4cb1..d1ce8b5 100644
--- a/parser.c
+++ b/parser.c
@@ -149,7 +149,7 @@ xmlParserEntityCheck(xmlParserCtxtPtr ctxt, size_t size,
        rep = xmlStringDecodeEntities(ctxt, ent->content,
                                  XML_SUBSTITUTE_REF, 0, 0, 0);
         --ctxt->depth;
-       if (ctxt->errNo == XML_ERR_ENTITY_LOOP) {
+       if (rep == NULL) {
            ent->content[0] = 0;
        }
 
@@ -7189,6 +7189,8 @@ xmlParseReference(xmlParserCtxtPtr ctxt) {
                   (ret != XML_WAR_UNDECLARED_ENTITY)) {
            xmlFatalErrMsgStr(ctxt, XML_ERR_UNDECLARED_ENTITY,
                     "Entity '%s' failed to parse\n", ent->name);
+            if (ent->content != NULL)
+                ent->content[0] = 0;
            xmlParserEntityCheck(ctxt, 0, ent, 0);
        } else if (list != NULL) {
            xmlFreeNodeList(list);