On the fsfs-format7 branch: undo r1461823.

* subversion/libsvn_subr/string.c
  (svn_stringbuf__morph_into_string): undo latest change

git-svn-id: https://svn.apache.org/repos/asf/subversion/branches/fsfs-format7@1462438 13f79535-47bb-0310-9956-ffa450edef68