shell: Only try to select an existing panel on startup

When selecting the panel on startup based on the "last-panel" settings,
we need to make sure that the panel exists.

Note that this is a special case which does not use the internal
set_active_panel_from_id API. Using it is currently not possible because
the API does not report back the error and we would end up not selecting
any panel.

shell/cc-shell-model.c

@@ -327,6 +327,30 @@ cc_shell_model_add_item (CcShellModel    *model,
   g_strfreev (keywords);
 }
 
+gboolean
+cc_shell_model_has_panel (CcShellModel *model,
+                          const char   *id)
+{
+  GtkTreeIter iter;
+  gboolean valid;
+
+  g_assert (id);
+
+  valid = gtk_tree_model_get_iter_first (model, &iter);
+  while (valid)
+    {
+      g_autofree gchar *panel_id = NULL;
+
+      gtk_tree_model_get (model, &iter, COL_ID, &panel_id, -1);
+      if (g_str_equal (id, panel_id))
+        return TRUE;
+
+      valid = gtk_tree_model_iter_next (model, &iter);
+    }
+
+  return FALSE;
+}
+
 gboolean
 cc_shell_model_iter_matches_search (CcShellModel *model,
                                     GtkTreeIter  *iter,

shell/cc-shell-model.h

@@ -98,6 +98,9 @@ void cc_shell_model_add_item (CcShellModel   *model,
                               GAppInfo       *appinfo,
                               const char     *id);
 
+gboolean cc_shell_model_has_panel (CcShellModel *model,
+                                   const char   *id);
+
 gboolean cc_shell_model_iter_matches_search (CcShellModel *model,
                                              GtkTreeIter  *iter,
                                              const char   *term);

shell/cc-window.c

@@ -756,7 +756,7 @@ cc_window_init (CcWindow *self)
   /* After everything is loaded, select the last used panel, if any,
    * or the first visible panel */
   id = g_settings_get_string (self->settings, "last-panel");
-  if (id != NULL && *id != '\0')
+  if (id != NULL && cc_shell_model_has_panel (self->store, id))
     cc_panel_list_set_active_panel (CC_PANEL_LIST (self->panel_list), id);
   else
     cc_panel_list_activate (CC_PANEL_LIST (self->panel_list));