native: don't push void result in Call

This was done in neo-project/neo#1693
for native calls. `OnPersist` script still uses `DROP` though
as value is pushed via `CheckReturn` logic for regular calls.

pkg/core/interop/context.go

@@ -82,6 +82,7 @@ type Method = func(ic *Context, args []stackitem.Item) stackitem.Item
 // MethodAndPrice is a native-contract method descriptor.
 type MethodAndPrice struct {
 	Func          Method
+	MD            *manifest.Method
 	Price         int64
 	RequiredFlags smartcontract.CallFlag
 }
@@ -123,6 +124,7 @@ func NewContractMD(name string) *ContractMD {
 // AddMethod adds new method to a native contract.
 func (c *ContractMD) AddMethod(md *MethodAndPrice, desc *manifest.Method, safe bool) {
 	c.Manifest.ABI.Methods = append(c.Manifest.ABI.Methods, *desc)
+	md.MD = desc
 	c.Methods[desc.Name] = *md
 	if safe {
 		c.Manifest.SafeMethods.Add(desc.Name)

pkg/core/interop/contract/call.go

@@ -77,8 +77,8 @@ func callExInternal(ic *interop.Context, h []byte, name string, args []stackitem
 		}
 		// use Jump not Call here because context was loaded in LoadScript above.
 		ic.VM.Jump(ic.VM.Context(), md.Offset)
-		ic.VM.Context().CheckReturn = true
 	}
+	ic.VM.Context().CheckReturn = true
 
 	md = cs.Manifest.ABI.GetMethod(manifest.MethodInit)
 	if md != nil {

pkg/core/native/interop.go

@@ -6,6 +6,7 @@ import (
 
 	"github.com/nspcc-dev/neo-go/pkg/core/interop"
 	"github.com/nspcc-dev/neo-go/pkg/core/state"
+	"github.com/nspcc-dev/neo-go/pkg/smartcontract"
 )
 
 // Deploy deploys native contract.
@@ -62,6 +63,8 @@ func Call(ic *interop.Context) error {
 		return errors.New("gas limit exceeded")
 	}
 	result := m.Func(ic, args)
-	ic.VM.Estack().PushVal(result)
+	if m.MD.ReturnType != smartcontract.VoidType {
+		ic.VM.Estack().PushVal(result)
+	}
 	return nil
 }