Convert the new filename to native separators before checking it

If a native separator was put in the new name when renaming a file name
via the file dialog then it would correctly fail. But if a non-native
one was used on Windows then it would cause the file to be moved
instead if the directory existed.

Change-Id: If01760b8c54a69b600c9a44c7509017be70d33e3
Reviewed-by: Stephen Kelly <stephen.kelly@kdab.com>

src/widgets/dialogs/qfilesystemmodel.cpp

@@ -850,7 +850,7 @@ bool QFileSystemModel::setData(const QModelIndex &idx, const QVariant &value, in
         return true;
 
     if (newName.isEmpty()
-        || newName.contains(QDir::separator())
+        || QDir::toNativeSeparators(newName).contains(QDir::separator())
         || !QDir(filePath(parent(idx))).rename(oldName, newName)) {
 #ifndef QT_NO_MESSAGEBOX
         QMessageBox::information(0, QFileSystemModel::tr("Invalid filename"),