[gnome-shell/gbsneto/polkit-fixup] polkit: Only unregister registered handles

[Georges Basile Stavracas Neto <gbsneto src gnome org>]

commit aeabebe5b3d3231ab4a8e83f65d3d1d70ea218a4
Author: Georges Basile Stavracas Neto <georges stavracas gmail com>
Date:   Thu Mar 22 11:11:38 2018 -0300

    polkit: Only unregister registered handles
    
    If the initialization fails for some reason, for example by
    running 'gnome-shell --replace', we should not crash because
    of an attempt of unregistering an unregistered agent handle.
    
    Fix that by checking if the handle is not NULL before calling
    the unregistering routines.
    
    https://gitlab.gnome.org/GNOME/gnome-shell/merge_requests/66

 src/shell-polkit-authentication-agent.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)
---
diff --git a/src/shell-polkit-authentication-agent.c b/src/shell-polkit-authentication-agent.c
index fd6c7913b..bca967fa1 100644
--- a/src/shell-polkit-authentication-agent.c
+++ b/src/shell-polkit-authentication-agent.c
@@ -318,8 +318,11 @@ shell_polkit_authentication_agent_unregister (ShellPolkitAuthenticationAgent *ag
   if (agent->current_request != NULL)
     auth_request_dismiss (agent->current_request);
 
-  polkit_agent_listener_unregister (agent->handle);
-  agent->handle = NULL;
+  if (agent->handle)
+    {
+      polkit_agent_listener_unregister (agent->handle);
+      agent->handle = NULL;
+    }
 }
 
 static void maybe_process_next_request (ShellPolkitAuthenticationAgent *agent);