[keyboard] When changing layouts, reset variant

- Need to update the variant that is in use, **and**
  explicitly update it in the widget, in order to re-load
  the keyboard image for the newly-selected layout+variant.

src/modules/keyboard/KeyboardLayoutModel.cpp

@@ -269,5 +269,6 @@ KeyboardVariantsModel::setVariants( QMap< QString, QString > variants )
     {
         m_list << ModelInfo { variants[ key ], key };
     }
+    m_currentIndex = -1;
     endResetModel();
 }

src/modules/keyboard/KeyboardPage.cpp

@@ -90,6 +90,7 @@ KeyboardPage::KeyboardPage( Config* config, QWidget* parent )
     connect( config->keyboardLayouts(), &KeyboardLayoutModel::currentIndexChanged, [ this ]( int index ) {
         ui->layoutSelector->setCurrentIndex( m_config->keyboardLayouts()->index( index ) );
         m_keyboardPreview->setLayout( m_config->keyboardLayouts()->key( index ) );
+        m_keyboardPreview->setVariant( m_config->keyboardVariants()->key( m_config->keyboardVariants()->currentIndex() ) );
     } );
 
     connect(