Steps to reproduce

1.  Create a dialog which contains an upload field as follows:

   form:
     properties:
       upload:
         $type: uploadField
         allowedMimeTypePattern: image/jpeg,image/gif,image/png,image/tiff

1.  Create the component and click on the "upload" button
2. Check that, on the dialog for selecting files, you can switch the option from "image/jpeg,image/gif,image/png,image/tiff" to ". all files"
3. Select ". all files" option, choose a file which doesn't match the mimeType pattern and upload it

Expected results

No ". all files" is displayed or, in any case, even if the option is displayed and other file types can be selected, the upload is prevented

Actual results

No filetype restriction exists

Workaround

N/A

Development notes

• reproduced under Windows
• reproduced in (Ubuntu) Linux - Firefox, Chrome.