create the RowOffsets structure in constructor of MatRepSym and store a local...

create the RowOffsets structure in constructor of MatRepSym and store a local pointer to it. This should preserve performance in Offset() method and there is no need to have the specialization of the structure. The problem reported by LHCb shoould then be fixed.


git-svn-id: http://root.cern.ch/svn/root/trunk@14298 27541ba8-7e3a-0410-8455-c3a389f83636