use-of-uninitialized-value in ReadPNGImage

use-of-uninitialized-value in ReadPNGImage: a task in MiMo-V2.6-RL-oss: Agentic RL Environments (MiMo RL release). MemorySanitizer: use-of-uninitialized-value in function ReadPNGImage in file graphicsmagick/coders/png.c