ast: Pre-allocate not found error.
ast: Pre-allocate not found error.

Minor improvements only:

benchmark                                        old allocs     new allocs     delta
BenchmarkConcurrency1-8                          2078256        2072250        -0.29%
BenchmarkConcurrency2-8                          2078463        2072465        -0.29%
BenchmarkConcurrency4-8                          2078816        2072814        -0.29%
BenchmarkConcurrency8-8                          2079300        2073345        -0.29%
BenchmarkConcurrency4Readers1Writer-8            2079022        2073033        -0.29%
BenchmarkConcurrency8Writers-8                   2078265        2072254        -0.29%

Signed-off-by: Teemu Koponen <514c492c49408016e397a2f741baa6dd9cf7f3be@styra.com>

open-policy-agent/opa,tsandall/opa,tsandall/opa,open-policy-agent/opa,tsandall/opa,open-policy-agent/opa,open-policy-agent/opa,open-policy-agent/opa,open-policy-agent/opa,tsandall/opa,tsandall/opa,tsandall/opa