_dbus_win_set_error_from_last_error: Always set the error
If we run out of memory while setting an error, we need to recover by setting the error to "out of memory" instead of the original error. Otherwise, the error indicator would be unset, breaking the rules of our error model.
@rhabacker, please could you test this on Windows? I think it will resolve the bug that was causing _DBUS_ASSERT_ERROR_XOR_BOOL
to fail in !228 (merged).