[libxml2] Fix NULL pointer deref in xmlTextReaderValidateEntity

[Nick Wellnhofer <nwellnhof src gnome org>]

commit 157cd3aed70845564e2ecc9754f3f826a3c9c65e
Author: Nick Wellnhofer <wellnhofer aevum de>
Date:   Sat Nov 24 15:46:00 2018 +0100

    Fix NULL pointer deref in xmlTextReaderValidateEntity
    
    Found by OSS-Fuzz.

 xmlreader.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)
---
diff --git a/xmlreader.c b/xmlreader.c
index 4461b36a..3acec759 100644
--- a/xmlreader.c
+++ b/xmlreader.c
@@ -1114,11 +1114,11 @@ xmlTextReaderValidateEntity(xmlTextReaderPtr reader) {
                continue;
            } else {
                /*
-                * The error has probably be raised already.
+                * The error has probably been raised already.
                 */
                if (node == oldnode)
                    break;
-               node = node->next;
+                goto skip_children;
            }
 #ifdef LIBXML_REGEXP_ENABLED
        } else if (node->type == XML_ELEMENT_NODE) {
@@ -1140,6 +1140,7 @@ xmlTextReaderValidateEntity(xmlTextReaderPtr reader) {
        } else if (node->type == XML_ELEMENT_NODE) {
            xmlTextReaderValidatePop(reader);
        }
+skip_children:
        if (node->next != NULL) {
            node = node->next;
            continue;