Fixes corruption of context
Fixes: 8835659dde6a4f7dcdf341de6a45c6c8-signal_sigsegv_1dce67b_4564_cov_2504444599_classical_22_16_1_14000_v3c_0_extend_0_29.wma
Found-by: Mateusz "j00ru" Jurczyk and Gynvael Coldwind
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>