Use the proper lower bound when doing saturation arithmetic.

Use the proper lower bound when doing saturation arithmetic.

16 bit signed integers have a range of [-32768, 32768).  The existing code
was using the interval (-32768, 32768) instead.  This patch fixes that.

Review: https://reviewboard.asterisk.org/r/2479/
........

Merged revisions 386929 from http://svn.asterisk.org/svn/asterisk/branches/1.8
........

Merged revisions 386930 from http://svn.asterisk.org/svn/asterisk/branches/11

git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@386931 65c4cc65-6c06-0410-ace0-fbb531ad65f3