Fix :restart with private browsing mode

CHANGELOG.asciidoc

@@ -49,6 +49,7 @@ Fixes
 ~~~~~
 
 - Fixed empty space being shown after tabs in the tabbar in some cases.
+- Fixed `:restart` in private browsing mode.
 
 v0.11.0
 -------

qutebrowser/app.py

@@ -634,7 +634,7 @@ class Quitter:
         # Save the session if one is given.
         if session is not None:
             session_manager = objreg.get('session-manager')
-            session_manager.save(session)
+            session_manager.save(session, with_private=True)
         # Open a new process and immediately shutdown the existing one
         try:
             args, cwd = self._get_restart_args(pages, session)