use-of-uninitialized-value in ff add png paeth prediction

use-of-uninitialized-value in ff add png paeth prediction: a task in MiMo-V2.6-RL-harbor-cyber: MiMo-V2.6-RL Cyber (Harbor) (Harbor dataset). MemorySanitizer: use-of-uninitialized-value in function ff add png paeth prediction in file ffmpeg/libavcodec/pngdec.c