Check if list of file globs matches at least one file

[sirex]

When given glob does not match any files, pyan3 exits without telling anything and generated an empty graph.

That might be confusing, when an incorrect file path is given. To avoid confusion, added additional check if glob matches at least one file.

Now it works like this:

> pyan3 --dot -f /tmp/graph.dot does/not/exist.py
Usage: pyan3 FILENAME... [--dot|--tgf|--yed]

pyan3: error: No files found matching given glob: does/not/exist.py

[Technologicat]

Merged. Thanks!