tdf#127461: fix data provider crashes

See bts provided in the bugtracker

Change-Id: I1cc38add93446f8372c80ca45962b04bfa627923
Reviewed-on: https://gerrit.libreoffice.org/78803
Tested-by: Jenkins
Reviewed-by: Julien Nabet <serval2412@yahoo.fr>

sc/source/ui/dataprovider/htmldataprovider.cxx

@@ -192,8 +192,21 @@ void HTMLFetchThread::execute()
     OString aID = OUStringToOString(maID, RTL_TEXTENCODING_UTF8);
     xmlXPathContextPtr pXmlXpathCtx = xmlXPathNewContext(pHtmlPtr);
     xmlXPathObjectPtr pXmlXpathObj = xmlXPathEvalExpression(BAD_CAST(aID.getStr()), pXmlXpathCtx);
+
+    if (!pXmlXpathObj)
+    {
+        xmlXPathFreeContext(pXmlXpathCtx);
+        return;
+    }
     xmlNodeSetPtr pXmlNodes = pXmlXpathObj->nodesetval;
 
+    if (!pXmlNodes)
+    {
+        xmlXPathFreeNodeSetList(pXmlXpathObj);
+        xmlXPathFreeContext(pXmlXpathCtx);
+        return;
+    }
+
     if (pXmlNodes->nodeNr == 0)
     {
         xmlXPathFreeNodeSet(pXmlNodes);