ff_id3v2_free_extra_meta: set the pointer pointing to extra_meta to NULL

Fixes ticket #3530.

Signed-off-by: Peter Ross <pross@xvid.org>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
(cherry picked from commit c94305ae23318c8956a30485cd5642829f4f16a9)
ff_id3v2_read: add option to limit ID3 magic number search

Several chunked formats (AIFF, IFF,DSF) store ID3 metadata within an 'ID3 '
chunk tag. If such chunks are stored sequentially, it is possible for the
ID3v2 parser to confuse the chunk tag for the ID3 magic number. e.g.

[1st chunk tag ('ID3 ') | chunk size] [ID3 magic number | metadata ...]
[2nd chunk tag ('ID3 ') | chunk size] [ID3 magic number | metadata ...]

Fixes ticket #3530.

Signed-off-by: Peter Ross <pross@xvid.org>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
(cherry picked from commit 5331773cc33ba26b9e26ace643d926219e46a17b)

Conflicts:
	libavformat/dsfdec.c
	libavformat/id3v2.c
avformat/avidec: Speed up keyframe detection code

Fixes Ticket3531

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
(cherry picked from commit 57fb570908df2e84b11635f12b5be1fb27f053eb)
ffprobe: fix scaling of vali in value_string() in case -prefix is selected

Fix trac ticket #3523.
(cherry picked from commit 1ba59b1cbeafe7cd28db04f772abd89eb7e4ce1e)
swresample: fix AV_CH_LAYOUT_STEREO_DOWNMIX input

Fixes Ticket 3542

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
(cherry picked from commit 291d464161a5bf3b566bc147f83e4242b0c18d74)