openvpnserv: always use W variant of RpcStringFree()

Probably not a real issue since it should always use the
W version in our case, but still unclean.

Fixes a cppcheck complaint.

Change-Id: I3d391016dcd3c66e58f3f05b356bcd419224acb1
Signed-off-by: Frank Lichtenheld <frank@lichtenheld.com>
Acked-by: Heiko Hund <heiko@openvpn.net>
Gerrit URL: https://gerrit.openvpn.net/c/openvpn/+/1671
Message-Id: <20260514091918.18197-1-gert@greenie.muc.de>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg36915.html
Signed-off-by: Gert Doering <gert@greenie.muc.de>

Author: flichtenheld

src/openvpnserv/interactive.c

@@ -3487,7 +3487,7 @@ RunOpenvpn(LPVOID p)
     swprintf(ovpn_pipe_name, _countof(ovpn_pipe_name),
              L"\\\\.\\pipe\\" _L(PACKAGE) L"%ls\\service_%lu_%ls", service_instance,
              GetCurrentThreadId(), pipe_uuid_str);
-    RpcStringFree(&pipe_uuid_str);
+    RpcStringFreeW(&pipe_uuid_str);
 
     /* make a security descriptor for the named pipe with access
      * restricted to the user and SYSTEM