Autodelete invalod nijie session

fixes #2324

app/logical/sources/strategies/nijie.rb

@@ -23,11 +23,18 @@ module Sources
       end
 
       def get
-        agent.get(url) do |page|
-          @artist_name, @profile_url = get_profile_from_page(page)
-          @image_url = get_image_url_from_page(page)
-          @tags = get_tags_from_page(page)
+        page = agent.get(url)
+
+        if page.search("div#header-login-container").any?
+          # Session cache is invalid, clear it and log in normally.
+          Cache.delete("nijie-session")
+          @agent = nil
+          page = agent.get(url)
         end
+
+        @artist_name, @profile_url = get_profile_from_page(page)
+        @image_url = get_image_url_from_page(page)
+        @tags = get_tags_from_page(page)
       end
 
     protected