Merge r1511353 from trunk:

 * r1511353
   svnmucc: Fix an assertion failure.
   Justification:
     It's an assertion failure.
   Votes:
     +1: danielsh, rhuijben, ivan


git-svn-id: https://svn.apache.org/repos/asf/subversion/branches/1.8.x@1513722 13f79535-47bb-0310-9956-ffa450edef68