adding a new function called expandFilePaths

adding a new function called expandFilePaths in Guard, that will return the complete file paths after filtering out zero byte files. (advantage is, user can have a work around with the file names before load if required) . Filtering out zero byte files can be used to avoid the empty-reduce left exception when there are no files to be processed. This check can be done by checking the size of the list returned by expandFilePaths.
[ User can either make use of the result of expandPaths or the result of expandFilePaths to be passed to the load function.]
This is changed... 
Also changed the code as per the above comments from @SamRoberts 
changed the function name to listNonEmptyFiles
changed the unnecessary usage of getFileSystem function.