Can't upload xlsx file

[sdecalom]

Preconditions (*)

1.OpenMage 19.4.15 and earlier and also 20.0.14 and earlier

Steps to reproduce (*)

1. When you use Mage_Uploader_Helper_File class
2. The $_mimeTypes variable have all mime-type of different type file
3. But for xlsx type, we don't have the mime-type in the variable

$uploader = new Mage_Core_Model_File_Uploader();
$uploader->setValidMimeTypes(Mage::helper('uploader/file')->getMimeTypesByExtensions("xlsx"));

Expected result (*)

1. File loaded successfully

Actual result (*)

1. Show popup box with this message Invalid MIME type.