libxml2: Check for xmlDocDumpFormatMemory() error case

Since this function needs to allocate memory, it might fail. Check that
the returned memory pointer is not NULL before trying to parse the
output.

Signed-off-by: Jouni Malinen <jouni@qca.qualcomm.com>

src/utils/xml_libxml2.c

@@ -212,6 +212,8 @@ char * xml_node_to_str(struct xml_node_ctx *ctx, xml_node_t *node)
 	xmlDocSetRootElement(doc, n);
 	xmlDocDumpFormatMemory(doc, &buf, &bufsiz, 0);
 	xmlFreeDoc(doc);
+	if (!buf)
+		return NULL;
 	pos = (char *) buf;
 	if (strncmp(pos, "<?xml", 5) == 0) {
 		pos = strchr(pos, '>');