getCurrentEvent throws if no event is in range

```
12:08:04.203Z ERROR tempea: Error getting temperatures
    TypeError: Cannot read property 'tz' of undefined
        at Object.getCurrentEvent (/src/controller/calendar/nextcloud.js:76:46)
        at process._tickCallback (internal/process/next_tick.js:68:7)
```

- getCurrentEvent should be surrounded by try/catch
- start and end from the event should be checked if present