watchdogd crashes while parsing state file with empty label

When parsing the following watchdogd.state file from an older version with empty string as lable, the process crashes.
```
Reset counter       : 32
Reset date          : 2021-09-07T08:45:36Z
PID                 : 0
Watchdog ID         : 0
Label               : 
Reset cause         : 7
Reset reason        : Unknown failure
```