Test pointers passed to copyrect for NULL.

diff --git a/windows/rect.c b/windows/rect.c
index b0c8f27..9bca84e 100644
--- a/windows/rect.c
+++ b/windows/rect.c
@@ -69,6 +69,8 @@
  */
 BOOL WINAPI CopyRect( RECT *dest, const RECT *src )
 {
+    if (!dest || !src)
+	return FALSE;
     *dest = *src;
     return TRUE;
 }