bug#22991: 25.0.92: C-u C-s does not display "Regexp I-search:" in the echo area

[Eli Zaretskii]

> Date: Fri, 11 Mar 2016 18:40:23 -0500
> From: Kaushal Modi <kaushal.modi@gmail.com>
> Cc: Eli Zaretskii <eliz@gnu.org>, "arturmalabarba@gmail.com" 
> <arturmalabarba@gmail.com>, 
>       "22991@debbugs.gnu.org" <22991@debbugs.gnu.org>
> 
> In that case, we will have to figure out why this condition was put as a high 
> priority to begin with. 
> 
> (cond ((equal regexp-function search-default-mode) "")

Clearly, because the intent was not to produce any prefix for the
default mode.