Backend exception causes infinite waiting

[ComiR]

Description

If the backend throws an exception (i.e. at the /neos/ui-services/flow-query endpoint), the UI doesn't show an error, it just waits for an answer indefinitely (i.e. the loading indicator/spinner shows forever).

Steps to Reproduce

1. create a subpage
2. remove the property uriPathSegment (directly in the database) [2]
3. open the parent page in the UI

[2] I created a page without the permission to edit it (the page created matched a NodeTreePrivilege). Therefore I ended up with a page node without properties.

Expected behavior

Show an error message and stop waiting.

Actual behavior

Infinite waiting.

Affected Versions

Neos: 3.3.9
UI: 1.0.9

[ComiR]

With UI 1.4.1, this is much better. It still is waiting indefinitely, but at least the error page gets shown in the content frame.

[grebaldi]

Closed in favor of #3477.