[#84] policy: Fix IteratorChainsByPrefix method

* If numeric mapping does not exists, then assign id to 0.
* Add check to unit-test.

Signed-off-by: Airat Arifullin <a.arifullin@yadro.com>

policy/policy_contract.go

@@ -115,7 +115,7 @@ func mapToNumeric(ctx storage.Context, kind Kind, name []byte) (mapped int, mapp
 	mKey := mapKey(kind, name)
 	numericID := storage.Get(ctx, mKey)
 	if numericID == nil {
-		return
+		return 0, false
 	}
 	mapped = numericID.(int)
 	mappingExists = true

tests/policy_test.go

@@ -32,6 +32,9 @@ func newPolicyInvoker(t *testing.T) *neotest.ContractInvoker {
 func TestPolicy(t *testing.T) {
 	e := newPolicyInvoker(t)
 
+	checkChainsIteratorByPrefix(t, e, policy.Namespace, "mynamespace", "ingress", [][]byte{})
+	checkChainsIteratorByPrefix(t, e, policy.Container, "cnr1", "ingress", [][]byte{})
+
 	// Policies are opaque to the contract and are just raw bytes to store.
 	p1 := []byte("chain1")
 	p2 := []byte("chain2")