fix amazonbackup script, trap on epipe exception for db backup

app/models/amazon_backup.rb

@@ -24,7 +24,7 @@ class AmazonBackup < ActiveRecord::Base
         AWS::S3::S3Object.store(File.basename(post.file_path), open(post.file_path, "rb"), Danbooru.config.amazon_s3_bucket_name, "Content-MD5" => base64_md5)
       end
 
-      if post.image? && File.exists?(post.preview_file_path)
+      if post.is_image? && File.exists?(post.preview_file_path)
         AWS::S3::S3Object.store("preview/#{post.md5}.jpg", open(post.preview_file_path, "rb"), Danbooru.config.amazon_s3_bucket_name)
       end
 
@@ -32,7 +32,7 @@ class AmazonBackup < ActiveRecord::Base
         AWS::S3::S3Object.store("large/#{post.md5}.jpg", open(post.large_file_path, "rb"), Danbooru.config.amazon_s3_bucket_name)
       end
 
-      AmazonBackup.update_id(last_id)
+      AmazonBackup.update_id(post.id)
     end
   rescue Exception => x
     # probably some network error, retry next time