Fix NoStrategyError during artist url normalization (#3382).

Fixes a bug from 9a3824a. When an artist entry is saved, `ArtistUrl.normalize`
is called on every URL, which calls `Sources::Site.new(url)`. This
raised NoStrategyError when an artist entry contained URLs that weren't
recognized by any strategy.

This also caused `Fetch source data` to fail in certain cases when it
attempted to find the artist.

app/models/artist_url.rb

@@ -18,7 +18,7 @@ class ArtistUrl < ApplicationRecord
       url = url.sub(%r!^http://pictures.hentai-foundry.com//!, "http://pictures.hentai-foundry.com/")
       begin
         url = Sources::Site.new(url).normalize_for_artist_finder!
-      rescue PixivApiClient::Error
+      rescue PixivApiClient::Error, Sources::Site::NoStrategyError
       end
       url = url.gsub(/\/+\Z/, "")
       url + "/"
@@ -75,6 +75,8 @@ class ArtistUrl < ApplicationRecord
     if !Sources::Site.new(normalized_url).normalized_for_artist_finder?
       self.normalized_url = self.class.normalize(url)
     end
+  rescue Sources::Site::NoStrategyError
+    self.normalized_url = self.class.normalize(url)
   end
 
   def initialize_normalized_url