fix(client): fix type assertion panic error

client/workflow/workflow.go

@@ -235,11 +235,11 @@ func (wf *Workflow) DoXa(dbConf dtmcli.DBConf, fn func(db *sql.DB) ([]byte, erro
 // Interceptor is the middleware for workflow to capture grpc call result
 func Interceptor(ctx context.Context, method string, req, reply interface{}, cc *grpc.ClientConn, invoker grpc.UnaryInvoker, opts ...grpc.CallOption) error {
 	logger.Debugf("grpc client calling: %s%s %v", cc.Target(), method, dtmimp.MustMarshalString(req))
-	wf, _ := ctx.Value(wfMeta{}).(*Workflow)
-	if wf == nil {
+	wfVal := ctx.Value(wfMeta{})
+	if wfVal == nil {
 		return invoker(ctx, method, req, reply, cc, opts...)
 	}
-
+	wf, _ := wfVal.(*Workflow)
 	origin := func() error {
 		ctx1 := dtmgimp.TransInfo2Ctx(ctx, wf.Gid, wf.TransType, wf.currentBranch, wf.currentOp, wf.Dtm)
 		err := invoker(ctx1, method, req, reply, cc, opts...)