Copying a TFormula doesn't preserve fLazyInitialization

When reading a TFormula from a file and making a copy of it before evaluation the TFormula is not initialized properly as `fLazyInitialization` is not copied to the new object.

I attached a minimal working example

$ root -l -q -x write.cxx 

Processing write.cxx...

$ root -l -q -x read.cxx 

Processing read.cxx...

original: 2

Error in <TFormula::DoEval>: Formula has error and  it is not properly initialized 

copy: nan