Fix closing with no last-visible-main-window

Fixes #1918

CHANGELOG.asciidoc

@@ -156,6 +156,7 @@ Fixed
 - The tabbar now displays correctly with the Adwaita Qt theme
 - The default `sk` keybinding now sets the commandline to `:bind` correctly
 - Fixed hang when using multiple spaces in a row with the URL completion
+- Fixed crash when closing a window without focusing it
 
 v0.8.3 (unreleased)
 -------------------

qutebrowser/mainwindow/mainwindow.py

@@ -492,12 +492,12 @@ class MainWindow(QWidget):
 
     def _do_close(self):
         """Helper function for closeEvent."""
-        last_visible = objreg.get('last-visible-main-window')
-        if self is last_visible:
-            try:
+        try:
+            last_visible = objreg.get('last-visible-main-window')
+            if self is last_visible:
                 objreg.delete('last-visible-main-window')
-            except KeyError:
-                pass
+        except KeyError:
+           pass
         objreg.get('session-manager').save_last_window_session()
         self._save_geometry()
         log.destroy.debug("Closing window {}".format(self.win_id))