OSV-2021-315 Global-buffer-overflow in Gfx::decode_frame

OSS-Fuzz report: https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=30507 Crash type: Global-buffer-overflow READ 4 Crash state: Gfx::decodeframe Gfx::GIFImageDecoderPlugin::frame Gfx::GIFImageDecoderPlugin::bitmap...