Fix signal handling when change_account in wot

src/sakia/gui/wot_tab.py

@@ -69,9 +69,12 @@ class WotTabWidget(QWidget, Ui_WotTabWidget):
         cancel_once_task(self, self.reset)
 
     def change_account(self, account, password_asker):
+        if self.account is not None:
+            self.account.certification_accepted.disconnect(self.refresh)
         self.account = account
         self.password_asker = password_asker
-        self.account.certification_accepted.connect(self.refresh)
+        if self.account is not None:
+            self.account.certification_accepted.connect(self.refresh)
 
     def change_community(self, community):
         self._auto_refresh(community)