Fixed handling of WM_MOUSEWHEEL messages in non-client space.

diff --git a/windows/message.c b/windows/message.c
index 7be0135..93f6b4c 100644
--- a/windows/message.c
+++ b/windows/message.c
@@ -504,7 +504,8 @@
     }
 
     pt = msg->pt;
-    if (hittest != HTCLIENT)
+    /* Note: windows has no concept of a non-client wheel message */
+    if (hittest != HTCLIENT && msg->message != WM_MOUSEWHEEL)
     {
         msg->message += WM_NCMOUSEMOVE - WM_MOUSEMOVE;
         msg->wParam = hittest;