Get rid of non-standard ERROR_UNKNOWN value.

diff --git a/server/file.c b/server/file.c
index 7c90f95..509a7c0 100644
--- a/server/file.c
+++ b/server/file.c
@@ -373,7 +373,7 @@
 #ifdef EOVERFLOW
     case EOVERFLOW: set_error( STATUS_INVALID_PARAMETER ); break;
 #endif
-    default:        perror("file_set_error"); set_win32_error( ERROR_UNKNOWN ); break;
+    default:        perror("file_set_error"); set_error( STATUS_UNSUCCESSFUL ); break;
     }
 }