libglusterfs/dict: fix infinite loop in dict_keys_join()

	 - missing "pairs = next" caused infinite loop

Change-Id: I9171be5bec051de6095e135d616534ab49cd4797
BUG: 905871
Signed-off-by: Vijaykumar Koppad <vijaykumar.koppad@gmail.com>
Reviewed-on: http://review.gluster.org/4723
Reviewed-by: Venky Shankar <vshankar@redhat.com>
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Anand Avati <avati@redhat.com>