Allow dringXrange to properly default to 10, as was done in 1.4.

dringXrange is a new feature that was added, and it attempted to default, but only when the option was specified.

(closes issue #12536)
Reported by: bjm
Patches:
      12536-dringXrange.diff uploaded by qwell (license 4)
Tested by: bjm


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@114922 65c4cc65-6c06-0410-ace0-fbb531ad65f3