Realtime queues failed to load queue information without queue member table

Previously, realtime queues could be loaded without defining the queue member
table.  This allowed for queue members to be dynamic, while the realtime
queue definitions could exist in some backing storage.  Revision 342223 broke
this when it changed the return value for realtime_multientry to return NULL
when no results are returned.  Previously, an empty ast_config object was
expected.

(closes issue ASTERISK-19170)
Reported by: Rene Mendoza
Tested by: Rene Mendoza
Patches: 
  rt_queue_member_patch.diff uploaded by Matt Jordan (license 6283)
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Merged revisions 350552 from http://svn.asterisk.org/svn/asterisk/branches/1.8
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Merged revisions 350553 from http://svn.asterisk.org/svn/asterisk/branches/10


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@350554 65c4cc65-6c06-0410-ace0-fbb531ad65f3