[Bug 5137] avifil32 limits itself to max of 1024 frames when writing avis

https://bugs.winehq.org/show_bug.cgi?id=5137

--- Comment #16 from Angus Lees  ---
I'm not in a position to retry my original code without a lot of work.  For
what it's worth however, your patch looks good to me from a simple visual
inspection.