Large key-median value causes error even though it is between key-minimum and key-maximum

[clkbug]

When a value exceeding 32 bits is set to key-median, the value will not be read correctly.

For example,

$ ./memtier_benchmark --key-pattern=G:G --key-minimum=10000000000 --key-maximum=30000000000 --key-median=20000000000
error: key-median must be between key-minimum and key-maximum.

(10000000000 is 34-bit value)

key-minimum and key-maximum are read correctly, but key-median is not.