use-of-uninitialized-value in UA base64

use-of-uninitialized-value in UA base64: a task in MiMo-V2.6-RL-oss: Agentic RL Environments (MiMo RL release). MemorySanitizer: use-of-uninitialized-value in function UA base64 in file open62541/deps/base64.c