Groupchat: Fix hide_groupchat_banner option

gajim/data/gui/groupchat_control.ui

@@ -99,12 +99,13 @@
                 <property name="visible">True</property>
                 <property name="can_focus">False</property>
                 <property name="margin_right">4</property>
+                <property name="hexpand">True</property>
                 <property name="orientation">vertical</property>
                 <child>
                   <object class="GtkEventBox" id="banner_eventbox">
                     <property name="name">GroupChatControl-BannerEventBox</property>
-                    <property name="visible">True</property>
                     <property name="can_focus">False</property>
+                    <property name="no_show_all">True</property>
                     <child>
                       <object class="GtkBox">
                         <property name="visible">True</property>

gajim/groupchat_control.py

@@ -122,8 +122,8 @@ class GroupchatControl(ChatControlBase):
         else:
             self.scale_factor = app.interface.roster.scale_factor
 
-        self.widget_set_visible(self.xml.get_object('banner_eventbox'),
-            app.config.get('hide_groupchat_banner'))
+        if not app.config.get('hide_groupchat_banner'):
+            self.xml.banner_eventbox.set_no_show_all(False)
 
         # muc attention flag (when we are mentioned in a muc)
         # if True, the room has mentioned us