Import Documents: Issues loading corpora

[ajdapretnar]

Describe the bug
Current master has an issue loading Conllu corpora with Import Documents. No such issue with latest release.

To Reproduce
Steps to reproduce the behavior:

1. Download (ParlaMint-SI-conllu)[https://www2.sistory.si/publikacije/material/parlamint/ParlaMint-SI-conllu.zip] data and unzip.
2. Load with Import Documents.

Expected behavior
Speed comparable to latest release.

Orange version:
3.40.dev

Text add-on version:
1.16.3.

Operating system:
OSX