synchronized with lua-nginx-module #23e69fb.

bugfix: ngx_http_lua_ffi_ssl_set_serialized_session(): avoided memory
leak when calling it repeatly.

Thanks spacewander for the upstream patch.

Author: thibaultcha

src/http/ngx_http_lua_ssl_session_fetchby.c

@@ -569,6 +569,7 @@ ngx_http_lua_ffi_ssl_set_serialized_session(ngx_http_request_t *r,
     ngx_ssl_conn_t                  *ssl_conn;
     ngx_connection_t                *c;
     ngx_ssl_session_t               *session = NULL;
+    ngx_ssl_session_t               *old_session;
     ngx_http_lua_ssl_ctx_t          *cctx;
 
     c = r->connection;
@@ -599,8 +600,13 @@ ngx_http_lua_ffi_ssl_set_serialized_session(ngx_http_request_t *r,
         return NGX_ERROR;
     }
 
+    old_session = cctx->session;
     cctx->session = session;
 
+    if (old_session != NULL) {
+        ngx_ssl_free_session(old_session);
+    }
+
     return NGX_OK;
 }