Following up on r1533994 and r1534037 resolve two off by one errors that were
originally hidden by making Windows handle the final '\0' byte. When r1534037
started passing the explicit length this handling was disabled.

* subversion/libsvn_subr/win32_xlate.c
  (svn_subr__win32_utf8_to_utf16,
   svn_subr__win32_utf16_to_utf8): Put '\0' in the buffer instead of one byte
     after the buffer.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1534082 13f79535-47bb-0310-9956-ffa450edef68