rpc: set transaction's script for test invocation

GetScriptContainer() interop can try to get this transaction and this attempt
will lead to hash calculation with transaction serialization, but transaction
can't be successfully serialized if it doesn't have a script set, so this
makes test invocations fail.

pkg/rpc/server/server.go

@@ -833,6 +833,7 @@ func (s *Server) invokeFunction(reqParams request.Params) (interface{}, *respons
 	if err != nil {
 		return nil, response.NewInternalServerError("can't create invocation script", err)
 	}
+	tx.Script = script
 	return s.runScriptInVM(script, tx), nil
 }
 
@@ -855,6 +856,7 @@ func (s *Server) invokescript(reqParams request.Params) (interface{}, *response.
 		}
 		tx.Cosigners = cosigners
 	}
+	tx.Script = script
 	return s.runScriptInVM(script, tx), nil
 }