Fix of no hcal energy for neutral protos

Fixes #505 (closed)

Logic was wrong when determining list of relevant (hcal) cell IDs.

The addCells function should be checking if in the vector the to-be-added cellID is already in it, if so skip adding. What it did is add only if it is already in there, of course if you start out with empty one, you'll never get any cells. Now it adds cellID if it the search for it reaches the end of the vector (a.k.a not being in there).

fyi: @graven