Nicoseiga: Add support for drm-served manga

app/logical/nico_seiga_api_client.rb

@@ -12,7 +12,10 @@ class NicoSeigaApiClient
       [api_response["id"]]
     elsif @work_type == "manga"
       manga_api_response.map do |x|
-        x["meta"]["source_url"].match(%r{/thumb/(\d+)\w}i).captures[0]
+        case x["meta"]["source_url"]
+        when %r{/thumb/(\d+)\w}i then Regexp.last_match(1)
+        when %r{nicoseiga\.cdn\.nimg\.jp/drm/image/\w+/(\d+)\w}i then Regexp.last_match(1)
+        end
       end
     end
   end

app/logical/sources/strategies/nico_seiga.rb

@@ -84,15 +84,10 @@ module Sources
       end
 
       def preview_urls
-        if manga_id.present?
-          image_urls.map do |img|
-            id = image_id_from_url(img)
-            "https://lohas.nicoseiga.jp/thumb/#{id}p"
-          end
-        elsif illust_id.present?
+        if illust_id.present?
           ["https://lohas.nicoseiga.jp/thumb/#{illust_id}i"]
         else
-          []
+          image_urls
         end
       end