add test case for empty (corrupted) files in the cache
add test case for empty (corrupted) files in the cache

cvmfs/cvmfs,DrDaveD/cvmfs,DrDaveD/cvmfs,Gangbiao/cvmfs,DrDaveD/cvmfs,cvmfs/cvmfs,cvmfs/cvmfs,DrDaveD/cvmfs,Gangbiao/cvmfs,Gangbiao/cvmfs,DrDaveD/cvmfs,djw8605/cvmfs,cvmfs/cvmfs,Gangbiao/cvmfs,DrDaveD/cvmfs,DrDaveD/cvmfs,djw8605/cvmfs,cvmfs/cvmfs,Gangbiao/cvmfs,cvmfs/cvmfs,djw8605/cvmfs,cvmfs/cvmfs,djw8605/cvmfs,djw8605/cvmfs