Disconnect from chat entry listener on tab closure

Before, more and more listeners got added to the chat entry, resulting in the bug of message text not being visible after posting.

Closes #25 (closed)

briar-gtk/briar_gtk/containers/main_window.py

@@ -96,7 +96,17 @@ class MainWindowContainer(Container):
         private_chat_widget = PrivateChatContainer(contact_name, contact_id)
         self.history_container.add(private_chat_widget)
         self.history_container.show_all()
-        self.chat_entry.connect("activate", private_chat_widget.send_message)
+
+        self._disconnect_chat_entry_signals()
+        self._chat_entry_signal_id = self.chat_entry.connect(
+            "activate", private_chat_widget.send_message
+        )
+
+    def _disconnect_chat_entry_signals(self):
+        if not hasattr(self, "_chat_entry_signal_id"):
+            return
+        self.chat_entry.disconnect(self._chat_entry_signal_id)
+        del self._chat_entry_signal_id
 
     def _no_chat_opened(self):
         return self.chat_placeholder.get_visible()