Merge r1469550 from trunk:

 * r1469550
   Fix a potential segfault in merge.
   Justification:
     It's a segfault (though I haven't bothered to make it happen)
   Votes:
     +1: breser, philip, rhuijben


git-svn-id: https://svn.apache.org/repos/asf/subversion/branches/1.8.x@1470806 13f79535-47bb-0310-9956-ffa450edef68