no apev2 metadata support for .aac files

[cyril]

Summary of the bug:
It's possible to write apev2 metadata and attach cover arts to .aac files using mp3tag v2.55a. But ffprobe doesn't detect any metadata nor cover art.

How to reproduce:

% ffprobe.exe music.aac
ffprobe version N-53758-g5711e4f Copyright (c) 2007-2013 the FFmpeg developers
  built on Jun  2 2013 02:33:52 with gcc 4.7.3 (GCC)
  configuration: --enable-gpl --enable-version3 --disable-w32threads --enable-av
isynth --enable-bzlib --enable-fontconfig --enable-frei0r --enable-gnutls --enab
le-iconv --enable-libass --enable-libbluray --enable-libcaca --enable-libfreetyp
e --enable-libgsm --enable-libilbc --enable-libmodplug --enable-libmp3lame --ena
ble-libopencore-amrnb --enable-libopencore-amrwb --enable-libopenjpeg --enable-l
ibopus --enable-librtmp --enable-libschroedinger --enable-libsoxr --enable-libsp
eex --enable-libtheora --enable-libtwolame --enable-libvo-aacenc --enable-libvo-
amrwbenc --enable-libvorbis --enable-libvpx --enable-libx264 --enable-libxavs --
enable-libxvid --enable-zlib
  libavutil      52. 34.100 / 52. 34.100
  libavcodec     55. 13.100 / 55. 13.100
  libavformat    55.  8.102 / 55.  8.102
  libavdevice    55.  2.100 / 55.  2.100
  libavfilter     3. 74.101 /  3. 74.101
  libswscale      2.  3.100 /  2.  3.100
  libswresample   0. 17.102 /  0. 17.102
  libpostproc    52.  3.100 / 52.  3.100
[aac @ 00000000026aef60] max_analyze_duration 5000000 reached at 5013333 microse
conds
[aac @ 00000000026aef60] Estimating duration from bitrate, this may be inaccurat
e
Input #0, aac, from 'music.aac':
  Duration: 41:06:02.08, bitrate: 6 kb/s
    Stream #0:0: Audio: aac, 48000 Hz, stereo, fltp, 6 kb/s

[cyril]

aac file with a cover art in apev2 metadata

[Elon Musk]

Fixed in d19d679e4b589b9c6b154674a8d2ebfd804be125.