Huge delay for completions when not sorting

[Martin Vaeth <martin@mvath.de>]

I would have expected that the line

zstyle ':completion:*' sort false

speeds things up if there is a huge number of completions.
However, quite the opposite is true.
If the above zstyle is in effect, the completion for the
artificial command "2" defined by the completion file

#compdef 2
local expl
_description a expl a
compadd "$expl[@]" - {1..40000}

takes ages. Inserting e.g. "touch" commands, it can be verified
that the delay happens _after_ the return of the completion function,
i.e. it is _not_ the compadd itself which is slow.

Moreover, without the _description line there is no delay.

If the 40000 is replaced by 10000, the delay "almost" vanishes
on my machine. Maybe the "critical" number is different on
other systems.