[FEM] fix pipeline recompute bug

- on recomputing scalar or warp filters the information about the field was lost.
  This is because the validity of an array was tested before it is actually filled

- also fix MSVC warning of using a C++ keyword as variable
- also avoid an unnecessary recompute after Elmer solver was run

src/Mod/Fem/femsolver/elmer/tasks.py

@@ -255,7 +255,6 @@ class Results(run.Results):
         # at the moment we scale the mesh back using Elmer
         # this might be changed in future, therefore leave this
         # self.solver.ElmerResult.scale(1000)
-        self.solver.ElmerResult.getLastPostObject().touch()
         self.solver.ElmerResult.recomputeChildren()
         self.solver.Document.recompute()