predicate_parse() adds two to nr_preds to reserve the terminal TRUE and FALSE entries. It also uses that increased value as the limit for parsed predicates. If the initial count is smaller than the number actually parsed, the program can fill the allocation and subsequent accesses can go past its end.
Keep nr_preds as the predicate limit and use a separate value for the allocation size. This leaves space for both terminal entries and a zeroed entry when parsing stops at the limit.