topdown: Fix panic in rand.intn function
topdown: Fix panic in rand.intn function

This commit just puts an error check in place to the panic from the
stdlib when rand.intn is called with an input < 1.

Signed-off-by: Torin Sandall <933af5bec0bc58056526d55ca6c7b45fcf14cc48@gmail.com>

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