Add option to error on zero-length files

Currently, scancode, when encountering a zero-length file (for example, [https://github.com/apache/incubator-openwhisk/blob/master/tests/dat/actions/empty.js](https://github.com/apache/incubator-openwhisk/blob/master/tests/dat/actions/empty.js)) under main OpenWhisk repo.), simply skips over the file (not performing any tests) and "passes" the file.

However, it would be good to have a command line flag that forces (causes) and error if zero-length files are found (not symbolic link files) and have a valid extensions (e.g., .js, .py, etc.).

Start by locating scancode's command-line option handling and the zero-length-file check. Verify the behavior with a valid-extension file such as empty.js, while excluding symbolic links; done means a new flag causes an error for matching zero-length files without changing the default behavior.

Written by the indexing model from the issue text.