check len of emparts before processing

[mslacken]

close #70

[littleyoda]

I would suggest parsing the protocol id and then pick only packages with measured values

see my PR for SMA-EM kellerza/hassio-sma-em#28

[mslacken]

As sma-em-measurements.py is just used for a quick check for what is going on in the network, it makes no difference how I ignore the stuff going on in the network.

[littleyoda]

At this point I would like to disagree. These types of scripts are often taken as a basis by other people. And so it would be good if a good solution were used directly and not a quick hack.

Let's see what the maintainer's opinion is.

[dervomsee]

@datenschuft Is the project still maintained? For me this commit fixes the issue.