use-of-uninitialized-value in IsPixelGray

use-of-uninitialized-value in IsPixelGray: a task in MiMo-V2.6-RL-oss: Agentic RL Environments (MiMo RL release). MemorySanitizer: use-of-uninitialized-value in function IsPixelGray in file imagemagick/MagickCore/pixel-accessor.h