[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

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  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()