Show unnamed calendar instead of null or empty name (#647)

    <string name="show_time_start_end_below">Start and end time below the event</string>

    <!-- Preferences -->

    <string name="preferences_calendar_no_display_name">Unnamed calendar</string>

    <string name="preferences_calendar_account">%1$s account</string>

    <string name="preferences_calendar_delete">Delete calendar</string>

    <string name="preferences_calendar_display_name">Change name</string>

    <string name="preferences_calendar_color">Color</string>

    <string name="preferences_calendar_visible">Display events</string>

    <string name="preferences_calendar_synchronize">Synchronize this calendar</string>

    <string name="preferences_calendar_color_warning_title">Warning</string>

    <string name="preferences_calendar_color_warning_message">Changing the color may be reverted when the calendar is synchronized again.\n\nIn DAVx⁵ \'Manage calendar colors\' can be disabled to prevent this.</string>

    <string name="preferences_calendar_color_warning_button">I understand</string>

    <string name="preferences_calendar_delete_message">Do you really want to delete this calendar?</string>

    <string name="preferences_calendar_delete_delete">Delete calendar</string>

    <string name="preferences_calendar_delete_cancel">Cancel</string>

    <string name="preferences_list_calendar_summary_sync_off">Not synchronized</string>

    <string name="preferences_list_calendar_summary_invisible">Events are not displayed</string>

    <string name="preferences_list_general">General settings</string>

    <string name="preferences_list_add_offline_button">Add calendar</string>

    <string name="preferences_list_add_offline_name">Name</string>

    <string name="preferences_list_add_offline_cancel">Cancel</string>

    <string name="preferences_calendar_color_warning_title">Warning</string>

    <string name="preferences_calendar_color_warning_message">Changing the color may be reverted when the calendar is synchronized again.\n\nIn DAVx⁵ \'Manage calendar colors\' can be disabled to prevent this.</string>

    <string name="preferences_calendar_color_warning_button">I understand</string>

    <string name="preferences_calendar_delete_message">Do you really want to delete this calendar?</string>

    <string name="preferences_calendar_delete_delete">Delete calendar</string>

    <string name="preferences_calendar_delete_cancel">Cancel</string>

    <string name="preferences_menu_about">About Etar</string>

    <string name="offline_account_name">Offline Calendar</string>

            }

            calendarPreference.apply {

                key = calendarUniqueKey

                title = calendar.displayName

                title = if (calendar.displayName.isNullOrBlank()) getString(R.string.preferences_calendar_no_display_name) else calendar.displayName

                fragment = CalendarPreferences::class.java.name

                order = if (calendar.isPrimary) 1 else 2 // primary calendar is first, others are alphabetically ordered below

                icon = getCalendarIcon(calendar.color, calendar.visible, calendar.syncEvents)