Revision 1587968

Fix a case of reading beyond allocated memory with SVN0, i.e. pre-1.4,
deltas.  This was identified by running svnadmin_tests.py 14 for FSFS
over ra_svn with svnserve running under valgrind.

* subversion/libsvn_delta/svndiff.c
  (decode_window): Allocate, copy and add terminating null for SVN0, remove
   incorrect comment for SVN1.