`pprod_term` may return incorrect pprod on hash collision

[Ovascos]

Function eq_pprod_hobj returns true for any pprod, as the returns statement is missing a comparison with the expected result o->r: https://github.com/SRI-CSL/yices2/blob/f06761440620cb803af6275baaefd3cbe880bb70/src/terms/terms.c#L1047