xapian-bridge C port

endlessm/eos-sdk#2463
Unless I misunderstand what you're saying, I would still need to look at `is_boolean` and fetch the right array, at which point the only difference with the rest of the function would be to avoid the `array_contains_pair()` check.
Since the array will be empty, the check is essentially almost a no-op, so I will leave the code as-is, because I don't think the extra complexity is worth it.