application: Take reference of GFile location when cloning window
Nautilus crashes under d45b820d when we open a second window and in both windows navigate to a common new location.
This is caused by incorrect reference management in action_clone_window, where neither nautilus_window_slot_get_location nor nautilus_window_slot_get_pending_location increases the ref count of the GFile location. g_autoptr would cause location to be prematurely freed.
Take the reference of location to allow g_autoptr to work correctly for all branches of action_clone_window.
Fixes #2858 (closed)