Follow-up to r1588899.

* subversion/libsvn_fs_fs/transaction.c
  (fnv1a_checksum_on_file_range): Don't NUL the read buffer
                                            *damn auto-complete*.

git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1588906 13f79535-47bb-0310-9956-ffa450edef68