bug#21785: 25.0.50; sort-fields fails if region ends in a newline and sort-paragraph fails if it doesn't

[Artur Malabarba <bruce.connor.am@gmail.com>]

I noticed this while writing tests for sort.el

With the following buffer contents (the text between the dashes,
including a final newline), issue `C-x h M-x sort-numeric-fields'.
You'll get the error that the last line doesn't have enough fields. I
think that error should not be thrown because of a final newline.

---------------------
1 hi
2 bye

----------------------

Meanwhile take the following buffer contents,
--------------------
paragraph 2

paragraph 1
--------------------

If you issue `sort-paragraphs' on the whole buffer, you'll get this:
--------------------
paragraph 1
paragraph 2

-------------------

In my opinion both behavior are bugs. But surely one of them is, as
the functions should be somewhat consistent on demanding final
newlines.