info-4.13 rings too many bells upon invalid search regexp

[Jim Meyering]

Hi,

I just did "info libc", then "s opendir (".
It used to work (texinfo-4.12), but now I get

    regexp error: Unmatched ( or \(

which is no problem.  I can adapt, of course.

However, I also got so many "BELL" (flash-screen)
alerts that my window flashed for so long that I
thought it was stuck in an infinite loop or printing
garbage, so I interrupted it quickly.  But I was
too impatient.  If I let it run its course, it stops
after about 5 seconds of screen flashing.

BTW, this is with

    $ ./ginfo --version
    info (GNU texinfo) 4.13

built from the tarball on an x86_64 F10.