Iqdb::Download.find_similar: simplify error handling.

Raise errors immediately to avoid deeply nested if-else statements.

app/logical/iqdb/download.rb

@@ -16,7 +16,8 @@ module Iqdb
     end
 
     def self.find_similar(source)
-      if Danbooru.config.iqdbs_server
+      raise NotImplementedError, "the IQDBs service isn't configured. Similarity searches are not available." unless enabled?
+
       url, ref = get_referer(source)
       params = {
         "key" => Danbooru.config.iqdbs_auth_key,
@@ -27,7 +28,8 @@ module Iqdb
       uri.query = URI.encode_www_form(params)
 
       resp = HTTParty.get(uri, Danbooru.config.httparty_options)
-        if resp.success?
+      raise "HTTP error code: #{resp.code} #{resp.message}" unless resp.success?
+
       json = JSON.parse(resp.body)
       if json.is_a?(Array)
         post_ids = json.map { |match| match["post_id"] }
@@ -40,12 +42,6 @@ module Iqdb
       else
         []
       end
-        else
-          raise "HTTP error code: #{resp.code} #{resp.message}"
-        end
-      else
-        raise NotImplementedError, "the IQDBs service isn't configured. Similarity searches are not available." unless enabled?
-      end
     end
   end
 end