Iqdb::Download.find_similar: simplify error handling.

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

app/logical/iqdb/download.rb

@@ -16,35 +16,31 @@ module Iqdb
     end
 
     def self.find_similar(source)
-      if Danbooru.config.iqdbs_server
-        url, ref = get_referer(source)
-        params = {
-          "key" => Danbooru.config.iqdbs_auth_key,
-          "url" => url,
-          "ref" => ref
-        }
-        uri = URI.parse("#{Danbooru.config.iqdbs_server}/similar")
-        uri.query = URI.encode_www_form(params)
+      raise NotImplementedError, "the IQDBs service isn't configured. Similarity searches are not available." unless enabled?
 
-        resp = HTTParty.get(uri, Danbooru.config.httparty_options)
-        if resp.success?
-          json = JSON.parse(resp.body)
-          if json.is_a?(Array)
-            post_ids = json.map { |match| match["post_id"] }
-            posts = Post.find(post_ids)
+      url, ref = get_referer(source)
+      params = {
+        "key" => Danbooru.config.iqdbs_auth_key,
+        "url" => url,
+        "ref" => ref
+      }
+      uri = URI.parse("#{Danbooru.config.iqdbs_server}/similar")
+      uri.query = URI.encode_www_form(params)
 
-            json.map do |match|
-              post = posts.find { |post| post.id == match["post_id"] }
-              match.with_indifferent_access.merge({ post: post })
-            end
-          else
-            []
-          end
-        else
-          raise "HTTP error code: #{resp.code} #{resp.message}"
+      resp = HTTParty.get(uri, Danbooru.config.httparty_options)
+      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"] }
+        posts = Post.find(post_ids)
+
+        json.map do |match|
+          post = posts.find { |post| post.id == match["post_id"] }
+          match.with_indifferent_access.merge({ post: post })
         end
       else
-        raise NotImplementedError, "the IQDBs service isn't configured. Similarity searches are not available." unless enabled?
+        []
       end
     end
   end