configure: Explicitly disable w32threads if the test for it fails

This avoids false positive enabling of w32threads if explicitly
requested on the command line, but dependencies are missing.
avformat/isom: free extradata  on failure to read it

Fixes use of uninitialized memory
Fixes: msan_uninit-mem_7f607d80f661_6965_mov00003.mqv
Found-by: Mateusz "j00ru" Jurczyk and Gynvael Coldwind
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
avformat: add ff_get_extradata()

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
avformat/adxdec: use ff_get_extradata()

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
avformat/aiffdec: use ff_get_extradata()

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
avformat/apc: use ff_get_extradata()

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
avformat/apetag: use ff_get_extradata()

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
avformat/avidec: use ff_get_extradata()

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
avformat/bink: use ff_get_extradata()

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
avformat/cafdec: use ff_get_extradata()

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
avformat/ffmdec: use ff_get_extradata()

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
avformat/flvdec: use ff_get_extradata()

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
avformat/idcin: use ff_get_extradata()

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
avformat/isom: use ff_get_extradata()

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
avformat/mov: use ff_get_extradata()

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
avformat/mpc: use ff_get_extradata()

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
avformat/mpc8: use ff_get_extradata()

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
avformat/nutdec: use ff_get_extradata()

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
avformat/nuv: use ff_get_extradata()

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
avformat/riffdec: use ff_get_extradata()

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>