Editor: upload file dialog behavior

[MariaKabanova]

Describe the Bug

Error message is shown when setting icon of unsupported file type in the editor

Steps to Reproduce

1. Go to any page
2. Click on “Set icon” and then upload file
3. Try to add not allowed file
4. You can see error popping up only for a few seconds:

Expected Behavior

Error message does not disappear

Actual Behavior

Error is shown for only a few seconds

Additional Information

The issue can be reproduced only in the editor, in Media Files we don't have this problem

Also maybe it makes sense to add supported image file types filter to the file picker dialog