[geary] FolderList.Tree: Fix search folder not appearing when selected

[Michael Gratton <mjog src gnome org>]

commit 652f77f76ad65dce0de5e36038cc2638e5e45f0a
Author: Michael Gratton <mike vee net>
Date:   Sat Mar 21 18:15:37 2020 +1100

    FolderList.Tree: Fix search folder not appearing when selected
    
    Fixes #744

 src/client/folder-list/folder-list-tree.vala | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/src/client/folder-list/folder-list-tree.vala b/src/client/folder-list/folder-list-tree.vala
index bd562eac..4a623a29 100644
--- a/src/client/folder-list/folder-list-tree.vala
+++ b/src/client/folder-list/folder-list-tree.vala
@@ -80,7 +80,7 @@ public class FolderList.Tree : Sidebar.Tree, Geary.BaseInterface {
     }
 
     private void on_entry_selected(Sidebar.SelectableEntry selectable) {
-        FolderEntry? entry = selectable as FolderEntry;
+        AbstractFolderEntry? entry = selectable as AbstractFolderEntry;
         if (entry != null) {
             this.selected = entry.folder;
             folder_selected(entry.folder);