[3.0] Some string recasts needed for exports

[sbulen]

While testing #8244 , I found two minor unrelated issues with the export. This PR addresses both.

When requesting html exports, the task would hang, leaving this in the PHP error log, and an entry in background_tasks:

PHP Fatal error:  Uncaught TypeError: hash_hmac(): Argument #2 ($data) must be of type string, int given in D:\wamp64\www\84van30\Sources\Tasks\ExportProfileData.php:1270
Stack trace:
#0 D:\wamp64\www\84van30\Sources\Tasks\ExportProfileData.php(1270): hash_hmac('sha1', 1, Object(SensitiveParameterValue))
#1 D:\wamp64\www\84van30\Sources\Tasks\ExportProfileData.php(930): SMF\Tasks\ExportProfileData->exportHtml()
#2 D:\wamp64\www\84van30\Sources\TaskRunner.php(565): SMF\Tasks\ExportProfileData->execute()
#3 D:\wamp64\www\84van30\Sources\TaskRunner.php(201): SMF\TaskRunner->performTask(Array)
#4 D:\wamp64\www\84van30\cron.php(32): SMF\TaskRunner->execute()
#5 {main}
  thrown in D:\wamp64\www\84van30\Sources\Tasks\ExportProfileData.php on line 1270

When requesting xml exports, the task would appear to complete, and generate an export file for download, but when you opened the export it contained this:

Fatal error:  Uncaught TypeError: hash_hmac(): Argument #2 ($data) must be of type string, int given in D:\wamp64\www\84van30\Sources\Actions\Profile\ExportDownload.php:176
Stack trace:
#0 D:\wamp64\www\84van30\Sources\Actions\Profile\ExportDownload.php(176): hash_hmac('sha1', 6, Object(SensitiveParameterValue))
#1 D:\wamp64\www\84van30\Sources\ActionTrait.php(44): SMF\Actions\Profile\ExportDownload->__construct()
#2 D:\wamp64\www\84van30\Sources\ActionTrait.php(55): SMF\Actions\Profile\ExportDownload::load()
#3 [internal function]: SMF\Actions\Profile\ExportDownload::call(6)
#4 D:\wamp64\www\84van30\Sources\Actions\Profile\Main.php(683): call_user_func(Array, 6)
#5 D:\wamp64\www\84van30\Sources\ActionTrait.php(55): SMF\Actions\Profile\Main->execute()
#6 [internal function]: SMF\Actions\Profile\Main::call()
#7 D:\wamp64\www\84van30\Sources\Forum.php(264): call_user_func(Array)
#8 D:\wamp64\www\84van30\index.php(149): SMF\Forum->execute()
#9 {main}
  thrown in D:\wamp64\www\84van30\Sources\Actions\Profile\ExportDownload.php on line 176

Tested in 3.0 with current GH code, both test OK.

[sbulen]

Note that SMF errors were not logged in the error log in either case above. One error was in the PHP log and one was in the actual resultant .html file itself.

I've seen a fair amount of this recently, lots of errors in the PHP log but not the SMF log.