Show the expander for tasks only when a matching child exists

Fixes the rest of GitHub issue #1207

Author: gycsaba96

GTG/core/tasks.py

@@ -710,6 +710,10 @@ def get_tree_model(self):
         return self.tree_model
 
 
+    def has_matching_children(self,task:Task):
+        return any(self.task_filter.do_match(c) for c in task.children)
+
+
     def set_filter(self,new_filter:Gtk.Filter):
         self.task_filter = new_filter
         self.task_filter.connect('changed',self._on_changed)

GTG/gtk/browser/task_pane.py

@@ -506,7 +506,8 @@ def show_start(binding, value, user_data=None):
 
         listitem.bindings = [
             item.bind_property('has_children', box, 'has_children', BIND_FLAGS),
-            item.bind_property('has_children', expander, 'hide-expander', BIND_FLAGS,lambda _,x: not x),
+            item.bind_property('has_children', expander, 'hide-expander', BIND_FLAGS
+                               ,lambda _,x: not self.filter_manager.has_matching_children(item)),
 
             item.bind_property('title', label, 'label', BIND_FLAGS),
             item.bind_property('excerpt', box, 'tooltip-text', BIND_FLAGS),