user32: Use root dialog for DM_SETDEFID/DM_GETDEFID in DefDlgProc.

dlls/user32/defdlg.c

@@ -188,6 +188,25 @@ static BOOL DEFDLG_SetDefButton( HWND hwndDlg, DIALOGINFO *dlgInfo, HWND hwndNew
 }
 
 
+static HWND root_dialog(HWND hwnd)
+{
+    while ((GetWindowLongA(hwnd, GWL_EXSTYLE) & WS_EX_CONTROLPARENT) &&
+           (GetWindowLongA(hwnd, GWL_STYLE) & (WS_CHILD|WS_POPUP)) == WS_CHILD)
+    {
+        HWND parent = GetParent(hwnd);
+
+        if (!DIALOG_get_info(parent, FALSE))
+            break;
+
+        hwnd = parent;
+
+        if (!(GetWindowLongA(hwnd, GWL_STYLE) & DS_CONTROL))
+            break;
+    }
+
+    return hwnd;
+}
+
 /***********************************************************************
  *           DEFDLG_Proc
  *
@@ -239,11 +258,17 @@ static LRESULT DEFDLG_Proc( HWND hwnd, UINT msg, WPARAM wParam,
             return 0;
 
         case DM_SETDEFID:
+            hwnd = root_dialog( hwnd );
+            dlgInfo = DIALOG_get_info( hwnd, FALSE );
+
             if (dlgInfo && !(dlgInfo->flags & DF_END))
                 DEFDLG_SetDefId( hwnd, dlgInfo, wParam );
             return 1;
 
         case DM_GETDEFID:
+            hwnd = root_dialog( hwnd );
+            dlgInfo = DIALOG_get_info( hwnd, FALSE );
+
             if (dlgInfo && !(dlgInfo->flags & DF_END))
             {
                 HWND hwndDefId;