Broken DMFile makes TiFlash abnormal

After TiFlash killed caused by OOM, the next time TiFlash start, it happened to this error:
```
<Error> Application: File not found: /data1/tidb-data/tiflash-9000//data/t_42707/stable/dmf_301/meta.txt
```

The directory on disk is like:
```
ls /data1/tidb-data/tiflash-9000//data/t_42707/stable/dmf_301/
60.null.dat  67.null.mrk  74.dat
```