Fix command prompt showing when using file input

Commit dd6a761 removes `set_echo(0)` when `infd` is not the standard
input, which will show command prompt while executing command from input
files. Adding it back fixes the issue.

console.c

@@ -586,6 +586,7 @@ static int cmd_select(int nfds,
                 interpret_cmd(cmdline);
             fflush(stdout);
         } else {
+            set_echo(0);
             char *cmdline = readline();
             if (cmdline)
                 interpret_cmd(cmdline);