Fix a bug: Occasionally the program crashes when executing run_builtin_cmd()

Signed-off-by: chenchacha <chen.chenchacha@foxmail.com>

Author: chenchacha

src/server.c

@@ -203,6 +203,7 @@ cJSON * run_builtin_cmd(jrpc_context * ctx, cJSON * params, cJSON *id)
 
 		int bak_fd = dup(STDOUT_FILENO);
    		int new_fd = dup2(fd[1], STDOUT_FILENO);
+ 		fflush(bak_fd);
                 func(argc, argv);
 		int size = read(fd[0], cmd_buff, CMD_BUFF- strlen(endstring) - 1);