[libxml2] Make schema validation fail with multiple top-level elements

[Nick Wellnhofer <nwellnhof src gnome org>]

commit 4f2aee18f6e2d40e58eb224f4f7935dc2400fe25
Author: Nick Wellnhofer <wellnhofer aevum de>
Date:   Mon May 4 14:03:52 2020 +0200

    Make schema validation fail with multiple top-level elements
    
    Closes #126.

 xmlschemas.c | 4 ++++
 1 file changed, 4 insertions(+)
---
diff --git a/xmlschemas.c b/xmlschemas.c
index a7804b78..81c47bc4 100644
--- a/xmlschemas.c
+++ b/xmlschemas.c
@@ -27933,6 +27933,10 @@ xmlSchemaVDocWalk(xmlSchemaValidCtxtPtr vctxt)
        VERROR(1, NULL, "The document has no document element");
        return (1);
     }
+    for (node = valRoot->next; node != NULL; node = node->next) {
+        if (node->type == XML_ELEMENT_NODE)
+            VERROR(1, NULL, "The document has more than one top element");
+    }
     vctxt->depth = -1;
     vctxt->validationRoot = valRoot;
     node = valRoot;