message: Fix: use TString.Data() instead of TString, check for failure of FOPEN
diff: @@ -1207,7 +1207,11 @@ void AliMagWrapCheb::SaveData(const char* outfile) const
  // writes coefficients data to output text file
  TString strf = outfile;
  gSystem->ExpandPathName(strf);
  - FILE* stream = fopen(strf,"w+");
  + FILE* stream = fopen(strf.Data(),"w+");
  + if (!stream) {
  + AliErrorF("Failed to open output file %s",strf.Data());
  + return;
  + }
  //
  // Sol part ---------------------------------------------------------
  fprintf(stream,"# Set of Chebyshev parameterizations for ALICE magnetic field\nSTART %s\n",GetName());
  