files-view: check if gdk_clipboard_read_value_async operation was cancelled in callback
Nautilus crashes if the user with a cut selection rapidly opens then closes a tab.
This is because update_cut_status_callback
is called after the files view has already been finalized. GIO guarantees that our callback will always be called even if we cancel the clipboard cancellable in dispose.
Check cancellation status in update_cut_status_callback
and proceed no further if cancelled.
Fixes #3434 (closed)