Update back/forward indicator on tab switches

qutebrowser/mainwindow/statusbar/backforward.py

@@ -34,6 +34,10 @@ class Backforward(textbase.TextBase):
             self.setText('')
             self.hide()
             return
+        self.on_tab_changed(tab)
+
+    def on_tab_changed(self, tab):
+        """Update the text based on the given tab."""
         text = ''
         if tab.history.can_go_back():
             text += '<'

qutebrowser/mainwindow/statusbar/bar.py

@@ -325,6 +325,7 @@ class StatusBar(QWidget):
         self.url.on_tab_changed(tab)
         self.prog.on_tab_changed(tab)
         self.percentage.on_tab_changed(tab)
+        self.backforward.on_tab_changed(tab)
         self.maybe_hide()
         assert tab.private == self._color_flags.private