OSV-2026-889 Use-of-uninitialized-value in vp8_compute_skin_block

OSS-Fuzz report: https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=520701729 Crash type: Use-of-uninitialized-value Crash state: vp8computeskinblock encodeframetodatarate vp8getcompresseddata...