[kcms/keyboard] Fix populating layouts when reloading config
Previously, it populated the internal list of layouts before reloading settings from kcfg. That lead to KCMKeyboardWidget::configureLayoutsChanged getting called for ticking the checkbox while the list of layouts was already nonempty, which is an invalid/unexpected state. In its confusion it cleared the list.
Just load kcfg settings first to avoid this.