On the fsfs-format7 branch: fix another merge artifact.

* subversion/libsvn_subr/cache-membuffer.c
  (svn_membuffer_cache_get): re-add lost return statement

git-svn-id: https://svn.apache.org/repos/asf/subversion/branches/fsfs-format7@1442504 13f79535-47bb-0310-9956-ffa450edef68