Tool checks if data has not fid

**Expected behaviour**
Dataset without FID is not valid data source for the tool. The tool could state that if the dataset does not have fid-field, it can not be handeled. 

**Current behaviour**
Accepts the data source and runs the analysis, QGIS gives a python error about the fid. 

**Describe alternatives you've considered**
Pre check on the data (or advice for the user). 

