Fix metatile label bug while saving

The metatile label only saved when the text field lost focus. But
saving doesn't cause the lineEdit to lose focus. This forces a
check whenever the tileset is saved.

include/ui/tileseteditor.h

@@ -95,6 +95,7 @@ private:
     void importTilesetTiles(Tileset*, bool);
     void importTilesetMetatiles(Tileset*, bool);
     void refresh();
+    void saveMetatileLabel();
     Ui::TilesetEditor *ui;
     History<MetatileHistoryItem*> metatileHistory;
     TilesetEditorMetatileSelector *metatileSelector = nullptr;