FFmpeg denial of service via division by zero in VVC decoder

Description

FFmpeg through 9.0.2 contains a division by zero vulnerability in the VVC decoder because ff_vvc_slice_rpl() fails to validate num_ref_idx_active against built reference list entries. Attackers can supply a crafted VVC bitstream whose excess reference indices yield a zero POC difference in ff_vvc_mv_scale(), crashing the decoding process.