fix confusing code in DecReports writer

The following discussion from !911 (merged) should be addressed:

• @graven started a discussion: (+1 comment)

  I think the above allen_number_of_active_lines[0] + 1 is wrong, as a v2 DecReport raw bank contains 2 32-bit integers (the TCK and the 'taskID') followed by N 32-bit integers where N is the number of lines. What I do not get is that the result of this should have been that the last decision would not be copied, and thus would be missing, but I would expect someone or some test would have caught that. So what is going on here?