(closes issue #13420)

(closes issue #13420)
Reported by: alex70
Patches:
      13420.13539.patch uploaded by murf (license 17)
Tested by: murf, awk

This fixes two problems: a spurious linefeed insertion
probably left over from pre-precomment times. Only
generated when category had no previous comments.

The other problem: Insertions could get the line-numbering
out of whack and generate negative line numbers, causing
chunks of line numbers to be emitted, on the scale of the
number of lines up to that point in the file. In such cases,
abort the looping, and all is well.

git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@157302 65c4cc65-6c06-0410-ace0-fbb531ad65f3