warning fixes in AnalysisTree

The MR fixes the following warnings (that can be seen here: https://cdash.gsi.de/buildSummary.php?buildid=432309):

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/home/cbmdock/cbmroot/analysis/common/analysis_tree_converter/CbmFsdHitsConverter.cxx: In member function 'virtual void CbmFsdHitsConverter::ProcessData(CbmEvent*)':
/home/cbmdock/cbmroot/analysis/common/analysis_tree_converter/CbmFsdHitsConverter.cxx:269:22: warning: comparison of integer expressions of different signedness: 'const unsigned int' and 'Int_t' {aka 'int'} [-Wsign-compare]
       if (trackIndex > cbm_global_tracks_->GetEntriesFast()) {
           ~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~