[libxml2] Fix xmlSchemaValidCtxtPtr reuse memory leak

[Nick Wellnhofer <nwellnhof src gnome org>]

commit b697d7bb5953faa2e699aafcca4058f4caffe734
Author: Greg Hildstrom <ghildstrom forcepoint com>
Date:   Tue Sep 4 16:48:15 2018 +0200

    Fix xmlSchemaValidCtxtPtr reuse memory leak
    
    When reusing an xmlSchemaValidCtxtPtr to validate multiple xml documents
    against the same schema, there is a memory leak in xmlschemas.c in
    xmlSchemaClearValidCtxt(). The vctxt->idcKeys and associated counters
    are not cleaned up in xmlSchemaClearValidCtxt() as they are in
    xmlSchemaFreeValidCtxt(). As a result, vctxt->idcKeys grows with each
    xmlValidateDoc() call that uses the same context and that memory is
    never freed. Similarly, vctxt->nbIdcKeys and vctxt->sizeIdcKeys
    increment and are never reset.
    
    Closes: #23

 xmlschemas.c | 11 +++++++++++
 1 file changed, 11 insertions(+)
---
diff --git a/xmlschemas.c b/xmlschemas.c
index 405f72ae..019988aa 100644
--- a/xmlschemas.c
+++ b/xmlschemas.c
@@ -27653,6 +27653,17 @@ xmlSchemaClearValidCtxt(xmlSchemaValidCtxtPtr vctxt)
        vctxt->nbIdcNodes = 0;
        vctxt->sizeIdcNodes = 0;
     }
+
+    if (vctxt->idcKeys != NULL) {
+       int i;
+       for (i = 0; i < vctxt->nbIdcKeys; i++)
+           xmlSchemaIDCFreeKey(vctxt->idcKeys[i]);
+       xmlFree(vctxt->idcKeys);
+       vctxt->idcKeys = NULL;
+       vctxt->nbIdcKeys = 0;
+       vctxt->sizeIdcKeys = 0;
+    }
+
     /*
     * Note that we won't delete the XPath state pool here.
     */