FIX: topic link extraction shouldn't fail when the parsed URL has no path

app/models/topic_link.rb

@@ -161,7 +161,7 @@ SQL
           added_urls << url
 
           unless TopicLink.exists?(topic_id: post.topic_id, post_id: post.id, url: url)
-            file_extension = File.extname(parsed.path)[1..10].downcase unless File.extname(parsed.path).empty?
+            file_extension = File.extname(parsed.path)[1..10].downcase unless parsed.path.nil? || File.extname(parsed.path).empty?
             begin
               TopicLink.create!(post_id: post.id,
                                 user_id: post.user_id,

spec/models/topic_link_spec.rb

@@ -230,7 +230,6 @@ http://b.com/#{'a' * 500}
       end
 
     end
-
   end
 
   describe 'internal link from pm' do
@@ -382,6 +381,11 @@ http://b.com/#{'a' * 500}
         expect(result).to eq({})
       end
     end
+
+    it "works with invalid link target" do
+      post = Fabricate(:post, raw: '<a href="http:geturl">http:geturl</a>', user: user, topic: topic, cook_method: Post.cook_methods[:raw_html])
+      expect { TopicLink.extract_from(post) }.to_not raise_error
+    end
   end
 
 end