Add atomic to mutable members of Csc4dSegmentMaker

http://goetz.web.cern.ch/goetz/mutable_2019-06-10.html#Muon,MuGirl_Csc

nightly/master/2019-06-10T2153:MuonSpectrometer/MuonReconstruction/MuonSegmentMakers/MuonSegmentMakerAlgs/CscSegmentMakers/src/Csc4dSegmentMaker.h +61

    59	  // Properties.
    60	  // Number of events dumped.
    61	  mutable int m_dumpcount;
    62	  mutable int m_dumped;
    63	  // Debug flags.
nightly/master/2019-06-10T2153:MuonSpectrometer/MuonReconstruction/MuonSegmentMakers/MuonSegmentMakerAlgs/CscSegmentMakers/src/Csc4dSegmentMaker.h +62

    60	  // Number of events dumped.
    61	  mutable int m_dumpcount;
    62	  mutable int m_dumped;
    63	  // Debug flags.
    64	  mutable bool m_dump;
nightly/master/2019-06-10T2153:MuonSpectrometer/MuonReconstruction/MuonSegmentMakers/MuonSegmentMakerAlgs/CscSegmentMakers/src/Csc4dSegmentMaker.h +64

    62	  mutable int m_dumped;
    63	  // Debug flags.
    64	  mutable bool m_dump;
    65	  double m_max_chisquare;
    66	  double m_max_slope_r;