ssl_write_certificate_request() can handle empty ca_chain
diff --git a/library/ssl_srv.c b/library/ssl_srv.c
index ee41633..9ba2294 100644
--- a/library/ssl_srv.c
+++ b/library/ssl_srv.c
@@ -972,7 +972,7 @@
     crt = ssl->ca_chain;
 
     total_dn_size = 0;
-    while( crt != NULL )
+    while( crt != NULL && crt->version != 0)
     {
         if( p - buf > 4096 )
             break;