Missing check for valid T & S ranges

[jkrasting]

The Wright 1997 equation of has a full parameter range of:

0 ≤ p ≤ 10⁸ Pa
−2° ≤ θ ≤ 40°C
0 ≤ S ≤ 40 psu

and a reduced range of:

0 ≤ p ≤ 5 × 10⁷ Pa
−2° ≤ θ ≤ 30°C
28 ≤ S ≤ 38 psu

Checks for these ranges should be added into the code.