bug#12399: 24.2.50; dired-do-touch doesn't recognize empty input in minibuffer

[Juri Linkov]

>>> There's another way to do that: check (eq val default), since the
>>> returned value will be `eq' to the `default' if the minibuffer was
>>> empty, whereas if it comes from a non-empty minibuffer it will at best
>>> be `equal'.
>>
>> I tried this in the following patch and it works.
>
> Installed.

I noticed the same problem in `dired-do-chmod' and fixed it the same way.