ssl_write_certificate_request() can handle empty ca_chain
(cherry picked from commit 21360ca4d45c47f16952fa1f75c21600c4e26d7e)

Conflicts:
	library/ssl_srv.c
diff --git a/library/ssl_srv.c b/library/ssl_srv.c
index 5f2891d..175a50c 100644
--- a/library/ssl_srv.c
+++ b/library/ssl_srv.c
@@ -505,7 +505,7 @@
     p += 2;
     crt = ssl->ca_chain;
 
-    while( crt != NULL )
+    while( crt != NULL && crt->version != 0)
     {
         if( p - buf > 4096 )
             break;