Fix compilation warning/error due to Gaudi::Property comparison
Both problem stem from the same problem of handling comparison of Gaudi::Property.
compilation warning in lhcb-head
- https://lbnightlies.cern.ch/logs/build/nightly/lhcb-head/1515/x86_64-centos7-gcc62-opt/Rec/
- 9dc6563b (comment 278042)
compilation error in lhcb-clang-test