Exception in SBAS MT26

[wdc-rsat]

An empty self.vtec array in decode_sbas_iono function causes a python3.13 runtime exception
within EGNOS bands 4 and 9 in this code
nigp = len(self.vtec[band])
I have temporarily fixed it with
` - nigp = len(self.vtec[band])

•    try:
  

•     nigp = len(self.vtec[band])
  

•    except:
  

•     nigp = 0
  

`
but maybe there is a better solution.

[hirokawa]

Thank you for feedback, I updated sbas.py on devel branch.