merge from trunk fix 47650 for avoid a crash when re-using the funciton object for fitting 

see http://root.cern.ch/viewvc?view=rev&revision=47650


git-svn-id: https://root.cern.ch/svn/root/branches/v5-34-00-patches@48244 27541ba8-7e3a-0410-8455-c3a389f83636
merge with trunk -  revision 48254  - see http://root.cern.ch/viewvc?rev=48254&root=root&view=rev


git-svn-id: https://root.cern.ch/svn/root/branches/v5-34-00-patches@48246 27541ba8-7e3a-0410-8455-c3a389f83636
merge with trunk -  revision 48245  - see http://root.cern.ch/viewvc?rev=48245&root=root&view=rev


git-svn-id: https://root.cern.ch/svn/root/branches/v5-34-00-patches@48247 27541ba8-7e3a-0410-8455-c3a389f83636