introduced in !40981, caught by
graphicplane_test.sup: "Normal Case" object redefinition was broken.
https://raw.githubusercontent.com/cubicibo/HandBrake/75ac11994fa4a32380d45c55a6add8344327773c/contrib/ffmpeg/A22-Add-cropping-and-graphic-plane-to-PGS-dec
Reference decoders (BD players) have a graphic plane to store the
rendered output. That plane is only refreshed by a window segment.
It is evaluated with the last palette and reused on palette updates.
This patch adds a conditionally writable graphic plane. The decoder
now differentiates appropria
