use-of-uninitialized-value in ReadSparse

use-of-uninitialized-value in ReadSparse: a task in MiMo-V2.6-RL-oss: Agentic RL Environments (MiMo RL release). MemorySanitizer: use-of-uninitialized-value in function ReadSparse in file matio/src/mat5.c