Convert MessageBox family functions to unicode

[Dmitry Timoshkov]

Hello.

Changelog:
    Restore setting of caption "Error".

--- cvs/hq/wine/windows/msgbox.c	Sun Oct 20 11:08:07 2002
+++ wine/windows/msgbox.c	Sun Oct 20 11:47:53 2002
@@ -61,8 +61,15 @@
     if (HIWORD(lpmb->lpszCaption)) {
        SetWindowTextW(hwnd, lpmb->lpszCaption);
     } else {
-       if (LoadStringW(lpmb->hInstance, LOWORD(lpmb->lpszCaption), buf, 256))
-	  SetWindowTextW(hwnd, buf);
+       static const WCHAR errorW[] = { 'E','r','r','o','r',0 };
+       UINT res_id = LOWORD(lpmb->lpszCaption);
+       if (res_id)
+       {
+           if (LoadStringW(lpmb->hInstance, res_id, buf, 256))
+               SetWindowTextW(hwnd, buf);
+       }
+       else
+           SetWindowTextW(hwnd, errorW);
     }
     if (HIWORD(lpmb->lpszText)) {
        lpszText = lpmb->lpszText;