Accessing a non-existant share shouldn't fail silently

[SystemKeeper]

What is going wrong?

Describe the bug
When accessing a share which is not available anymore a white page with nextcloud header is displayed instead of an error.

To Reproduce
Steps to reproduce the behavior:

1. Create a poll
2. Create a public link
3. Remove the public link
4. Try to access the now removed link

Expected behavior
A clear and concise description of what you expected to happen.

Screenshots
Show a error message like nextcloud does when accessing a non-existant file-share:

Current behaviour:

The ajax request does already fail with 404:

Information about your polls installation

Polls version? 1.1.5

Fresh installation or update from a prior version (from which one)?
Update

How did you install this version?(Appstore or describe installation)
Manually

Information about your Instance of Nextcloud/ownCloud

Nextcloud or ownCloud? NC

Which Version? 17.0.2