Problems when parsing an empty file

I originally got an error 

    /Library/Ruby/Gems/1.8/gems/flog-3.2.1/lib/flog.rb:297:in `flog_ruby!': undefined method `mass' for nil:NilClass (NoMethodError)
    	from /Library/Ruby/Gems/1.8/gems/flog-3.2.1/lib/flog.rb:266:in `flog_ruby'
    	from /Library/Ruby/Gems/1.8/gems/flog-3.2.1/lib/flog.rb:256:in `flog'
    	from /Library/Ruby/Gems/1.8/gems/flog-3.2.1/lib/flog.rb:253:in `each'
    	from /Library/Ruby/Gems/1.8/gems/flog-3.2.1/lib/flog.rb:253:in `flog'
    	from /Library/Ruby/Gems/1.8/gems/flog-3.2.1/bin/flog:13
    	from /usr/bin/flog:19:in `load'
    	from /usr/bin/flog:19

Which I tracked down to a .rb file in my tree being empty. This pull requests catches that error and possibly other unprocessable files.

It's a bit quick and dirty and may not be the best long term solution though.