Skip counting log length when parseLogRow return nil (#176)

Fix:
![image](/attachments/93e29bc0-3599-4f7e-8b90-512562a5d711)

Regression of #149, `LogLength` could be incorrect.

It may be related to https://github.com/go-gitea/gitea/issues/24458

Reviewed-on: https://gitea.com/gitea/act_runner/pulls/176
Reviewed-by: Zettat123 <zettat123@noreply.gitea.io>
Reviewed-by: wxiaoguang <wxiaoguang@noreply.gitea.io>

internal/pkg/client/client.go

@@ -9,6 +9,8 @@ import (
 )
 
 // A Client manages communication with the runner.
+//
+//go:generate mockery --name Client
 type Client interface {
 	pingv1connect.PingServiceClient
 	runnerv1connect.RunnerServiceClient