[Bugfix] Fix reddit bugs v2 (#82)

* Ensured thumbnail is converted to jpg before embedding

* Ensured media indexing doesn't fail if an upload date can't be parsed

lib/pinchflat/downloading/download_option_builder.ex

@@ -66,7 +66,7 @@ defmodule Pinchflat.Downloading.DownloadOptionBuilder do
           acc ++ [:write_thumbnail, convert_thumbnail: "jpg"]
 
         {:embed_thumbnail, true} ->
-          acc ++ [:embed_thumbnail]
+          acc ++ [:embed_thumbnail, convert_thumbnail: "jpg"]
 
         _ ->
           acc