DO NOT MERGE: Add validation for eternal enities

https://bugzilla.gnome.org/show_bug.cgi?id=780691

Bug: 36556310
Change-Id: I9450743e167c3c73af5e4071f3fc85e81d061648
(cherry picked from commit 5209ab424d9e1880853a67fd1c07a65716c4233d)

parser.c

diff --git a/parser.c b/parser.c
index 53a6b7f..b197dfc 100644
--- a/parser.c
+++ b/parser.c
@@ -8123,6 +8123,14 @@
 	    if (xmlPushInput(ctxt, input) < 0)
 		return;
 	} else {
+	    if ((entity->etype == XML_EXTERNAL_PARAMETER_ENTITY) &&
+	        ((ctxt->options & XML_PARSE_NOENT) == 0) &&
+	        ((ctxt->options & XML_PARSE_DTDVALID) == 0) &&
+	        ((ctxt->options & XML_PARSE_DTDLOAD) == 0) &&
+	        ((ctxt->options & XML_PARSE_DTDATTR) == 0) &&
+	        (ctxt->replaceEntities == 0) &&
+	        (ctxt->validate == 0))
+	        return;
 	    /*
 	     * TODO !!!
 	     * handle the extra spaces added before and after