id3v2: fix skipping extended header in id3v2.4

In v2.4, the length includes the length field itself.
(cherry picked from commit ddb4431208745ea270dce8fce4cba999f0ed4303)

Conflicts:

	libavformat/id3v2.c

Signed-off-by: Anton Khirnov <anton@khirnov.net>
1 file changed