Fix some unicode->ascii calls.

diff --git a/windows/mdi.c b/windows/mdi.c
index da5d96f..afc2daa 100644
--- a/windows/mdi.c
+++ b/windows/mdi.c
@@ -1705,8 +1705,8 @@
             break;
         case SC_RESTORE:
         case SC_MINIMIZE:
-            SetWindowLongA( hwnd, GWL_STYLE,
-                            GetWindowLongA( hwnd, GWL_STYLE ) | WS_SYSMENU );
+            SetWindowLongW( hwnd, GWL_STYLE,
+                            GetWindowLongW( hwnd, GWL_STYLE ) | WS_SYSMENU );
             break;
         case SC_MAXIMIZE:
             if (ci->hwndChildMaximized == hwnd)