add missing self on lookup of file_matches


git-svn-id: https://root.cern.ch/svn/root/trunk@49080 27541ba8-7e3a-0410-8455-c3a389f83636
Import revision 49081 from the v5-34-00 patch branch:
Avoid accessing fLeaves out of bounds


git-svn-id: https://root.cern.ch/svn/root/trunk@49082 27541ba8-7e3a-0410-8455-c3a389f83636