Fix #5002: "Urls url has already been taken" when submitting duplicate urls with different capitalization

Fix URLs being normalized after checking for duplicates rather than
before, which meant that URLs that differed in capitalization weren't
detected as duplicates.

app/logical/artist_finder.rb

@@ -149,7 +149,7 @@ module ArtistFinder
   # @param url [String] the artist profile URL
   # @return [Array<Artist>] the list of matching artists
   def find_artists(url)
-    url = ArtistUrl.normalize(url)
+    url = ArtistUrl.normalize_normalized_url(url)
     artists = []
 
     while artists.empty? && url.size > 10