Function pT_reg4 returns region number instead of an error code

[UvidusNox]

Thank you for providing this library.
I believe there is a small inconsistency in the following function:
r4::region4::pT_reg4

Specifically line #24:

pub fn pT_reg4(p: f64, T: f64, o_id: i32) -> f64 {
    if T == TC_WATER && p == PC_WATER {
        return Td_reg3(TC_WATER, DC_WATER, o_id);
    } else {
        return 4.0 as f64;
    }
}

The function returns the region number as f64, instead of an error INVALID_VALUE or similar.
Is this behaviour intentional?
Thank you