afh: Fix fd leak.

afh: Fix fd leak.

The main() function of para_afh obtains the open file descriptor from
mmap_full_file() which is then passed to compute_afhi(). If this file
descriptor is never closed, we have an fd leak.

Unfortunately it depends on the audio format handler whether fd
gets closed or not: the mp3 audio format handler closes it through
libid3tag's id3_file_close() while all other audio format handlers
leave it open.

Fix this by changing mp3_get_id3() to operate on a copy of the fd
instead so that the original fd remains open. The newly added close()
in afh.c thus fixes the fd leak and never closes an invalid fd.