An out-of-bounds memory write could occur in GetSingleLoop() when the
condition (pointCells->GetNumberOfIds() < 2). GetSingleLoop() adds a
line cell to complete a loop in this case, but that fact was not
accounted for in the caller when allocating the argument for the
lineBool array. Fixed that, and cleaned up the code by using a
std::vector instead of an array. Finally, added a test that exercises
the condition to make sure it is tested.