[JUNGFRAU][CORRECT] Fix/store roi only if defined
Compare changes
```
```
```
```
```
```
```
```
```
```
```
```
```
```
```
```
```
```
```
```
```
```
```
```
```
```
```
A bug was introduced here https://git.xfel.eu/detectors/pycalibration/-/merge_requests/762/diffs that lead to creating CONTROL and INSTRUMENT sections for ROI even if none was defined.