Warning should be generated when an invalid Linux zip file is detected

[EmperorArthur]

In linux.py, an invalid zip file is ignored. Instead, a Warning should be generated, or as per the comment, an exception should be generated.

This behavior led to hours of confusion thinking that the system was not working. It was only until I instrumented the code that I realized that I had somehow generated an empty ".dwarf" file!

As a new user, these sorts of problems are not obvious, especially because I was not even sure I put the zip file in the correct location.