Fixed wrong layer name getting edited when switching maps

When double-clicking a layer (which opens the inline editor for renaming
the layer) and then switching to another map, the layer at the same
index in the new map would get the name in the inline editor.

To avoid this, explicitly commit the data before switching the model.

Closes #1396

src/tiled/layerdock.cpp

@@ -244,9 +244,15 @@ void LayerView::setMapDocument(MapDocument *mapDocument)
 {
     if (mMapDocument) {
         mMapDocument->disconnect(this);
+
         QItemSelectionModel *s = selectionModel();
         disconnect(s, SIGNAL(currentRowChanged(QModelIndex,QModelIndex)),
                    this, SLOT(currentRowChanged(QModelIndex)));
+
+        if (QWidget *w = indexWidget(currentIndex())) {
+            commitData(w);
+            closeEditor(w, QAbstractItemDelegate::NoHint);
+        }
     }
 
     mMapDocument = mapDocument;