bug#11984: 24.1; segfault while deleting a window

[Chong Yidong]

martin rudalics <rudalics@gmx.at> writes:

>> But for long-term safety, I think
>> decode_any_windows had better signal an error if the window's frame
>> isn't live.  But I'm not sure if there's any subtle reliance in existing
>> code on allowing window functions to be called for windows on dead
>> frames---anyone know?
>
> Maybe the best way to find out is to install such a change?

Done in the trunk.