Dropdown menu: uncaught exception when pressing arrow up/down

Summary

In a boolean dropdown menu in edit mode, pressing the up/down arrow "too often" leads to an unhandled exception:

The Firefox console says:

TypeError: we.getInstance(...) is null
    dataApiKeydownHandler https://crm.indiscale.com/webinterface/1662134770/webcaosdb.dist.js:11
    n https://crm.indiscale.com/webinterface/1662134770/webcaosdb.dist.js:11
webcaosdb.dist.js:3615:13
Uncaught TypeError: we.getInstance(...) is null
    dataApiKeydownHandler https://crm.indiscale.com/webinterface/1662134770/webcaosdb.dist.js:11
    n https://crm.indiscale.com/webinterface/1662134770/webcaosdb.dist.js:11
webcaosdb.dist.js:11:45979
Uncaught TypeError: we.getInstance(...) is null
    dataApiKeydownHandler https://crm.indiscale.com/webinterface/1662134770/webcaosdb.dist.js:11
    n https://crm.indiscale.com/webinterface/1662134770/webcaosdb.dist.js:11
webcaosdb.dist.js:11:45979

​ Also uploading files does not show the uploaded element in the dropdown menu any more.

Expected Behavior

No exception. Uploaded files are shown.

Actual Behavior

Exception popup appears. Uploaded files are only shown upon reload.

Steps to Reproduce the Problem

1. Enter edit mode
2. Edit a boolean Property
3. Press up/down arrow on keyboard "too often".

Specifications

• Version: Latest demo
• Platform: Firefox 91.13.0esr on Debian 11.

Possible fixes

-/-

DoD

• review and merge !78 (merged)