hevc: Reject impossible dependent tile

The tile 0 cannot depend on a previous one.
Prevent an out of array bound load in ff_hevc_cabac_init().

Fixes: asan_heap-oob_e3a924_1630_DBLK_A_MAIN10_VIXS_2.bit
Found-by: Mateusz "j00ru" Jurczyk and Gynvael Coldwind

Reviewed-by: Guillaume Martres <smarter@ubuntu.com>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
hevc: Bound check slice_qp

The T-REC-H.265-2013044 page 79 states they have to be into the range
[-s->sps->qp_bd_offset, 51].

Fixes: asan_stack-oob_eae8e3_9522_WP_MAIN10_B_Toshiba_3.bit
Found-by: Mateusz "j00ru" Jurczyk and Gynvael Coldwind

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
avcodec/hevc: Check entry point arrays for malloc failure

Fixes null pointer dereference
Fixes: signal_sigsegv_e1d3b6_2192_DBLK_F_VIXS_2.bit
Found-by: Mateusz "j00ru" Jurczyk and Gynvael Coldwind
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>