Fix crash when selecting a shiva filter or generator

[Boudewijn Rempt]

On Tuesday 10 November 2009, Cyrille Berger wrote:
> hi,
> 
> Those two patches fixes crashes when selecting some of the shiva filters
>  that have already been used, and also when reconfiguring some of the
>  generators.
> 
> I would like to backport them to branch/2.1.
> 

I trust your expertise here, so it's okay as far as I'm concerned.

-- 
Boudewijn Rempt | http://www.valdyas.org