refactor IsRedlineAtEnd

should be no logic change, just added a comment as to
what is going on here and ready for extension

Change-Id: Ibf1a3893ece9a09ad342bb06f39e119c1340e0db
consider following redline as well

a) In word each range that character properties affect are just stored by their
end. So the range is from the last end to the current one.

b) In word the paragraph end marker is a real character, in writer it is not.

c) So for redlining if a paragraph is redlined, but the previous one is not
then the redlining propes of the 2nd para will affect the end marker of the
previous one if the previous char properties do not include the para end mark.

We were currently handing the case where a paragraph end mark *is* inside
redlining and including it in the char property range, but we were not
considering the case where the paragraph end mark is *not* inside redlining
but the following paragraph *is*

to get the end of the previous paragraph not part of the following paragraph
character run, we emit an empty char section of it for this case.

Change-Id: I816335067f60d1d9332bfdb1117fb1448b564972