server: Make module handles always 64-bit.

server/window.c

diff --git a/server/window.c b/server/window.c
index 1922baa..a24b2d6 100644
--- a/server/window.c
+++ b/server/window.c
@@ -480,7 +480,7 @@
     win->style          = 0;
     win->ex_style       = 0;
     win->id             = 0;
-    win->instance       = NULL;
+    win->instance       = 0;
     win->is_unicode     = 1;
     win->is_linked      = 0;
     win->is_layered     = 0;