The string is created with %llu
. See: https://github.com/bitcoin/bitcoin/blob/7fcf53f7b4524572d1d0c9a5fdc388e87eb02416/src/leveldb/db/db_impl.cc#L1436-L1437
So it seems odd to silently accept when parsing: whitespace, a sign character, trailing chars, overflow, ….
Fix that by using the stricter ToIntegral.