CVE-2026-49346: fix integer overflow in image plane allocation size

CVE-2026-49346: fix integer overflow in image plane allocation size

Origin: upstream, https://github.com/strukturag/libde265/commit/8a1b5cf212f78e1c77cb46eb5d56e492a9336eb8
Bug: https://github.com/strukturag/libde265/security/advisories/GHSA-vv8h-932h-7r86
Bug-Debian: https://bugs.debian.org/1140431
Applied-Upstream: 1.1.0

Large SPS dimensions with 16-bit bit depth overflow the 32-bit allocation
size in de265_image_get_buffer(); the wrapped ~1 KB allocation is later
written with the full plane size, corrupting the heap.

Gbp-Pq: Name CVE-2026-49346.patch