Avoid using uninitialized output size variable
Avoid using uninitialized output size variable

Make sure we initialize `avail_out`; if the memory happened to be 0, this would trigger an infinite loop.
alhowaidi/cvmfsNDN,Gangbiao/cvmfs,Moliholy/cvmfs,djw8605/cvmfs,alhowaidi/cvmfsNDN,djw8605/cvmfs,DrDaveD/cvmfs,Moliholy/cvmfs,DrDaveD/cvmfs,alhowaidi/cvmfsNDN,alhowaidi/cvmfsNDN,DrDaveD/cvmfs,cvmfs/cvmfs,Gangbiao/cvmfs,trshaffer/cvmfs,reneme/cvmfs,cvmfs/cvmfs,cvmfs/cvmfs,alhowaidi/cvmfsNDN,reneme/cvmfs,cvmfs/cvmfs,cvmfs/cvmfs,DrDaveD/cvmfs,cvmfs/cvmfs,trshaffer/cvmfs,Gangbiao/cvmfs,Gangbiao/cvmfs,Gangbiao/cvmfs,Moliholy/cvmfs,djw8605/cvmfs,DrDaveD/cvmfs,Moliholy/cvmfs,cvmfs/cvmfs,DrDaveD/cvmfs,djw8605/cvmfs,djw8605/cvmfs,trshaffer/cvmfs,reneme/cvmfs,reneme/cvmfs,reneme/cvmfs,DrDaveD/cvmfs,trshaffer/cvmfs,trshaffer/cvmfs,Moliholy/cvmfs