Missing attachment button for attachments of a known type

If there was a known formatter for the attachment's mime type, the attachment
content was shown inline, without the attachment button, instead of it being
shown collapsed and with the corresponding button. All that caused by a variable
overwrite and a related memory leak.

em-format/e-mail-formatter-attachment.c

@@ -332,8 +332,6 @@ emfe_attachment_format (EMailFormatterExtension *extension,
 			size = g_memory_output_stream_get_data_size (
 				G_MEMORY_OUTPUT_STREAM (content_stream));
 
-			buffer = g_string_sized_new (size);
-
 			g_string_append_printf (
 				buffer,
 				"<tr><td colspan=\"2\">"