This reverts commit 8dd7b34, reversing
changes made to 369f0b2.

…n-less container

Containers with no template icon get /plugins/dynamix.docker.manager/images/question.png
recorded as their icon in the webui-info registry (DockerClient.php L346). removeContainer()
then unlinks that recorded path when cache flags are set, deleting the shared fallback from
the docroot for the whole system until the next reboot. CA Docker Auto-Update triggers this
whenever it updates an icon-less container.

Also quote and guard the container-list onerror fallback (this.onerror=null) so a missing
fallback degrades to one failed request per image instead of an endless 404 retry loop.

Fixes #2691

(cherry picked from commit 6f28eb6)

…delete-shared-default-docker-icon-questionpng

fix: backport shared default docker icon fix to 7.3