CVE-2026-33021 libsixel: Use-after-free in sixel_encoder_encode_bytes()

libsixel is a SIXEL encoder/decoder implementation derived from kmiya's sixel. Versions 1.8.7 and prior contain a use-after-free vulnerability in sixelencoderencodebytes because sixelframeinit stores the caller-owned pixel buffer pointer directly in frame-pixels without making a defensive copy...