Follow-up to r1461707:

* subversion/libsvn_fs/fs-loader.c
  (svn_fs_commit_txn): Initialise 'txn_root' if SVN_DEBUG is defined but
   PACK_AFTER_EVERY_COMMIT is not. Fixes crashes in tests when compiling
   without -DPACK_AFTER_EVERY_COMMIT.

Found by: philip


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1461714 13f79535-47bb-0310-9956-ffa450edef68