vm: process OLDPUSH1 at the context level

The only usecase for this opcode is single-byte verification scripts.

pkg/vm/context.go

@@ -74,6 +74,12 @@ func (c *Context) Next() (opcode.Opcode, []byte, error) {
 
 	var numtoread int
 	switch instr {
+	case opcode.OLDPUSH1:
+		// OLDPUSH1 is used during transition to NEO3 in verification scripts.
+		// FIXME remove #927
+		if len(c.prog) == 1 {
+			return opcode.PUSH1, nil, nil
+		}
 	case opcode.PUSHDATA1:
 		if c.nextip >= len(c.prog) {
 			err = errNoInstParam

pkg/vm/vm.go

@@ -553,10 +553,6 @@ func (v *VM) execute(ctx *Context, op opcode.Opcode, parameter []byte) (err erro
 		val := int(op) - int(opcode.PUSH1) + 1
 		v.estack.PushVal(val)
 
-	case opcode.OLDPUSH1:
-		// FIXME remove this after Issue transactions will be removed
-		v.estack.PushVal(1)
-
 	case opcode.PUSH0:
 		v.estack.PushVal([]byte{})