- Fix a problem in TChain::LoadTree.

  When a entry is asked which is not available in all the trees of
  the chain (i.e. entryNumber > chain.GetEntries() ), the LoadTree() function
  deletes the currently file opened and returns an error code. That's perfect,
  but when deleting the file the "fFile" pointer is not set to 0, therefore
  in the destructor of the class
      if (fFile) delete fFile;
  calls the TFile destructor a second time generating a SEGV
  (Thanks Manuel Sanchez for reporting)


git-svn-id: http://root.cern.ch/svn/root/trunk@91 27541ba8-7e3a-0410-8455-c3a389f83636