Bugfix :: Metatdata Season Thumbnail : Fixes bug that attempted retrieval of non-existent season 0 (Special) and skipped last season when a show lacks a season 0.

This bug was discovered by luxmoggy; see [forum post](http://www.sickbeard.com/forums/viewtopic.php?f=4&t=6572).

Some show are missing thumbnails for the last season. This is because when retrieving the thumbnails a list of seasons is created using number of seasons and a range(0..n) (e.g. [0, 1, 2, 3, 4, 5]. When a show lacks a season 0, it will still create the list using the same range  starting point; Thereby creating a list containing a non-existent season 0 and missing the last season ([0, 1, 2, 3, 4]).

This patch drops creating a new list in favor of using the already existing list.