lib-master, util: Consistently truncate tabescaped input at the first…

… NUL

The NULs are supposed to come tab-escaped, so there's no need to support
actual NUL characters. The previous code truncated at NULs, but could
have kept appending more data to the value. This could have produced
somewhat random results.

src/lib-master/master-login.c

@@ -299,7 +299,7 @@ static void master_login_postlogin_input(struct master_login_postlogin *pl)
 				conn_error(conn, "close(client) failed: %m");
 			pl->client->fd = fd;
 		}
-		str_append_n(pl->input, buf, ret);
+		str_append_data(pl->input, buf, ret);
 	}
 
 	len = str_len(pl->input);

src/util/script-login.c

@@ -44,7 +44,7 @@ static void client_connected(struct master_service_connection *conn)
 	instr = t_str_new(1024);
 	ret = fd_read(conn->fd, buf, sizeof(buf), &fd);
 	while (ret > 0) {
-		str_append_n(instr, buf, ret);
+		str_append_data(instr, buf, ret);
 		if (buf[ret-1] == '\n' &&
 		    strchr(str_c(instr), '\n')[1] != '\0') {
 			str_truncate(instr, str_len(instr)-1);