fixed bug in StRoot/StFemtoEvent/StFemtoTrack.cxx in GetMassSqr method mBeta -> GetBeta()

StRoot/StFemtoEvent/StFemtoTrack.cxx

@@ -130,9 +130,10 @@ Float_t StFemtoTrack::GetMassSqr() const {
 
   //Calculate squared mass of the track via TOF beta measurement
   Float_t mSqr = -999.;
+  Float_t beta = GetBeta();
   if(mBeta > 0.) {
     Float_t ptot = TMath::Sqrt(mMomX*mMomX + mMomY*mMomY + mMomZ*mMomZ);
-    mSqr = ptot*ptot * (1./(mBeta*mBeta) - 1.);
+    mSqr = ptot*ptot * (1./(beta*beta) - 1.);
   }
 
   return mSqr;