Database preset import doesn't work on Windows

When trying to import a Database activity preset file on a Windows server, the import fails as the importer filters away part of the imported file's filename part way through.

To replicate this, you will need a server on Windows.

Replication steps:

1. Log in as admin/teacher
2. Navigate to a course
3. Create a Database activity
4. Click on the Preset tab
5. Upload a preset zip file (I will attach an example)
6. Work through the import process

Expected result: The import should complete successfully

Actual result: The import fails in the final stage and reports a 'cannotimport' error (with little detail).

On a Windows server, the preset file is passed to the server with a .tmp extension (eg. tem2464.tmp). This is able to be extracted to a directory (eg. tem2464.tmp_extracted) without trouble, but on line 219, the extracted preset directory is received as a form field and the PARAM_ALPHANUMEXT filter is applied, which removes dots (eg. tem2464tmp_extracted). When the script checks that the directory exists, this fails and the import fails.

$presetdir = $CFG->tempdir.'/forms/'.required_param('directory', PARAM_ALPHANUMEXT);

Replacing this filter with the more appropriate PARAM_FILE filter allows dots through and allows the preset import to complete.