clear artist urls before saving url string (fixes #3731)

app/models/artist.rb

@@ -181,11 +181,9 @@ class Artist < ApplicationRecord
     def save_urls
       if url_string && saved_change_to_url_string?
         Artist.transaction do
+          self.urls.clear
           self.urls = url_string.scan(/[^[:space:]]+/).uniq.map do |url|
-            # need to do these shenanigans to properly handle prefixes
-            aurl = self.urls.find_or_create_by(url: ArtistUrl.strip_prefixes(url))
-            aurl.update(url: url)
-            aurl
+            self.urls.find_or_create_by(url: url)
           end
         end
       end

test/unit/artist_test.rb

@@ -49,6 +49,13 @@ class ArtistTest < ActiveSupport::TestCase
       refute(@artist.urls[0].is_active?)
     end
 
+    should "allow activating a url" do
+      @artist = Artist.create(name: "blah", url_string: "-http://monet.com")
+      @artist.update(url_string: "http://monet.com")
+      assert_equal(1, @artist.urls.count)
+      assert(@artist.urls[0].is_active?)
+    end
+
     should "should have a valid name" do
       @artist = Artist.new(:name => "-blah")
       @artist.save