server: Don't save bogus chunk table for aac files.

server: Don't save bogus chunk table for aac files.

The audio file selector stores the chunk table of each audio file
as an osl disk object. Since the aac audio format handler employs
dynamic chunks, these on-disk chunk tables of aac files will never
be consulted for streaming. They exist only for consistency with the
other audio formats and should be empty.

Due to a mis-computation of the chunk table size in the callback of
the add command we happen to store the serialized lopsub parse result
as the chunk table.

This is a benign bug since it only affects the ls command, and only
if -l=c is given to print the chunk table.