[libxml2] Fix inappropriate fetch of entities content

[Daniel Veillard <veillard src gnome org>]

commit b1d34de46a11323fccffa9fadeb33be670d602f5
Author: Daniel Veillard <veillard redhat com>
Date:   Mon Mar 14 17:19:44 2016 +0800

    Fix inappropriate fetch of entities content
    
    For https://bugzilla.gnome.org/show_bug.cgi?id=761430
    
    libfuzzer regression testing exposed another case where the parser would
    fetch content of an external entity while not in validating mode.
    Plug that hole

 parser.c |   16 +++++++++++++++-
 1 files changed, 15 insertions(+), 1 deletions(-)
---
diff --git a/parser.c b/parser.c
index c424fc1..f6d652e 100644
--- a/parser.c
+++ b/parser.c
@@ -2861,7 +2861,21 @@ xmlStringLenDecodeEntities(xmlParserCtxtPtr ctxt, const xmlChar *str, int len,
                ctxt->nbentities += ent->checked / 2;
            if (ent != NULL) {
                 if (ent->content == NULL) {
-                   xmlLoadEntityContent(ctxt, ent);
+                   /*
+                    * Note: external parsed entities will not be loaded,
+                    * it is not required for a non-validating parser to
+                    * complete external PEreferences coming from the
+                    * internal subset
+                    */
+                   if (((ctxt->options & XML_PARSE_NOENT) != 0) ||
+                       ((ctxt->options & XML_PARSE_DTDVALID) != 0) ||
+                       (ctxt->validate != 0)) {
+                       xmlLoadEntityContent(ctxt, ent);
+                   } else {
+                       xmlWarningMsg(ctxt, XML_ERR_ENTITY_PROCESSING,
+                 "not validating will not read content for PE entity %s\n",
+                                     ent->name, NULL);
+                   }
                }
                ctxt->depth++;
                rep = xmlStringDecodeEntities(ctxt, ent->content, what,