fix in_tail with v11 text_parser spec (time with nil without @time_key)

`in_tail` should emit with `Time.now.to_i` for records without any times or invalid `@time_key` data.

This is `in_tail` 's spec, but not a spec of `text_parser`.  `text_parser` should do only parsing, and what time will be used on emit by plugin is what plugin author should think about.