avcodec/takdec: Skip last p2 sample (which is unused)

Fixes out of array read
Fixes: cb3f38b08b4541523974667c7d1eee9e/asan_heap-oob_2659e18_9838_021fd5cd635bf76cede6398cd9ecbcdd.tak

Found-by: Mateusz "j00ru" Jurczyk and Gynvael Coldwind
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
