Fix for ROOT-7477 - bin/thisroot.csh problems with empty ROOTSYS
Fix for ROOT-7477 - bin/thisroot.csh problems with empty ROOTSYS

tc3t/qoot,tc3t/qoot,tc3t/qoot,tc3t/qoot,tc3t/qoot,tc3t/qoot,tc3t/qoot,tc3t/qoot,tc3t/qoot,tc3t/qoot