Do a sanity check on locations to prevent a crash

[rickprice]

Sanity check locations value in json dictionary to handle when the value does not exist.

Fix for #55
Fix for #37

[Scarygami]

Thanks for taking care of this topic.
The issue I see with this approach, is that this will just create empty output files, when choosing the wrong input file.
I think it would be useful to put out a message in case locations is missing, to make clear why this has happened.

[Forge36]

While this prevents the crash it doesn't parse the data. I'm with Scarygami that this doesn't get at the heart of the request for those issues.