Fix potential log panic (#82)
If a job uses a [reusable workflow](https://docs.github.com/en/actions/using-workflows/workflow-syntax-for-github-actions#example-of-jobsjob_iduses), the job's steps sequence will be empty.
But in log reporter, we don't check the length of `r.state.Steps`, which may cause panic.
``` go
if v, ok := entry.Data["stepNumber"]; ok {
if v, ok := v.(int); ok {
step = r.state.Steps[v]
}
}
```
Reviewed-on: https://gitea.com/gitea/act_runner/pulls/82
Reviewed-by: Lunny Xiao <xiaolunwen@gmail.com>
Co-authored-by: Zettat123 <zettat123@gmail.com>
Co-committed-by: Zettat123 <zettat123@gmail.com>