[stable20] Don't throw a 500 when importing a broken ics reminder file

[backportbot-nextcloud]

backport of #24964

[faily-bot]

🤖 beep boop beep 🤖

Here are the logs for the failed build:

Status of 969: failure

acceptance-users

• tests/acceptance/features/users.feature:47

Show full log

 Scenario: users navigation without disabled users # /drone/src/tests/acceptance/features/users.feature:47
Given I act as Jane # ActorContext::iActAs()
And I am logged in as the admin # LoginPageContext::iAmLoggedInAsTheAdmin()
And I open the User settings # SettingsMenuContext::iOpenTheUserSettings()
And I open the "Disabled users" section # AppNavigationContext::iOpenTheSection()
And I see that the list of users contains the user disabledUser # UsersSettingsContext::iSeeThatTheListOfUsersContainsTheUser()
And I open the actions menu for the user disabledUser # UsersSettingsContext::iOpenTheActionsMenuOf()
Row for user disabledUser in Users Settings could not be found
Actions menu for user disabledUser in Users Settings could not be found (NoSuchElementException)
And I see that the "Enable user" action in the disabledUser actions menu is shown # UsersSettingsContext::iSeeTheAction()
When I click the "Enable user" action in the disabledUser actions menu # UsersSettingsContext::iClickTheAction()
Then I see that the section "Disabled users" is not shown # AppNavigationContext::iSeeThatTheSectionIsNotShown()
When I open the User settings # SettingsMenuContext::iOpenTheUserSettings()
Then I see that the section "Disabled users" is not shown # AppNavigationContext::iSeeThatTheSectionIsNotShown()