Previously these two dialplan functions would issue warnings and
return failure when an empty string is used as the argument. Now
they will not issue a warning and will successfully return an
empty string.
ASTERISK-23911 #close
Reported by: Matt Jordan
Review: https://reviewboard.asterisk.org/r/3745/
git-svn-id: https://origsvn.digium.com/svn/asterisk/branches/1.8@418641 65c4cc65-6c06-0410-ace0-fbb531ad65f3