fix(editor,terminal): Correctly restore log buffer and cursor position

A regresion was introduced by #81 where the log buffer was not being
    restored when there was no modification after describing from the
    log buffer. This has been reworked and now the function `on_done` is
    always called not only when there are lines in the buffer giving the
    responsibility to check the nilness on the `on_done` function.

    There was a bug also when restoring cursor position which was being
    wiped when the buffer was closed which is not actually what we want

lua/jj/ui/terminal.lua

@@ -148,7 +148,6 @@ function M.close_terminal_buffer()
 	-- Otherwise close the buffer
 	buffer.close(state.buf)
 	state.buf_cmd = nil
-	state.cursor_restore_pos = nil
 	state.chan = nil
 	state.job_id = nil
 end