CVE-2026-54240, CVE-2026-54241: fix pixel-accessor integer overflow

CVE-2026-54240, CVE-2026-54241: fix pixel-accessor integer overflow

Origin: upstream, https://github.com/strukturag/libde265/commit/bdca87569b9c63c2a7054d90ae4462dbb78d159a
Bug: https://github.com/strukturag/libde265/security/advisories/GHSA-ccfw-29x7-rrx3
Bug: https://github.com/strukturag/libde265/security/advisories/GHSA-j2qq-x2xq-g9wr
Applied-Upstream: 1.1.1

The image pixel accessors computed xpos + ypos*stride in signed 32-bit
arithmetic; frames with width*height > INT32_MAX wrap the offset and the
returned pointer lands far outside the buffer (OOB read/write). Widen
stride/offset math to 64 bits and store validated SPS dimensions in
uint16_t.

Gbp-Pq: Name CVE-2026-54240_CVE-2026-54241.patch