Add debug output in case of assertion failure
diff --git a/library/ssl_cli.c b/library/ssl_cli.c
index 1312e01..d309f6d 100644
--- a/library/ssl_cli.c
+++ b/library/ssl_cli.c
@@ -2297,6 +2297,7 @@
     if( ssl->session_negotiate->peer_cert == NULL )
     {
         /* Should never happen */
+        MBEDTLS_SSL_DEBUG_MSG( 1, ( "should never happen" ) );
         return( MBEDTLS_ERR_SSL_INTERNAL_ERROR );
     }
     peer_pk = &ssl->session_negotiate->peer_cert->pk;