Crash Climbing Spawned Ladder

**Ladder unit wasn't a level unit**

```
<>...ult_player_unit/states/player_character_state_helper.lua:713: Ladder unit wasn't a level unit<>
<> [1] =[C]: in function assert
[2] @scripts/unit_extensions/default_player_unit/states/player_character_state_helper.lua:713: in function set_is_on_ladder
[3] @scripts/unit_extensions/default_player_unit/states/player_character_state_climbing_ladder.lua:67: in function on_enter
[4] @scripts/unit_extensions/generic/generic_state_machine.lua:53: in function update
[5] @scripts/unit_extensions/generic/generic_character_state_machine_extension.lua:89: in function update
[6] @scripts/entity_system/systems/extension_system_base.lua:112:in function
[7] @scripts/entity_system/entity_system_bag.lua:56: in function update
[8] @scripts/entity_system/entity_system.lua:455: in function system_update
[9] @scripts/entity_system/entity_system.lua:424: in function update
[10] @scripts/game_state/state_ingame.lua:982: in function hook_chain
[11] @scripts/mods/vmf/modules/core/hooks.lua:180: in function update
[12] @foundation/scripts/util/state_machine.lua:145: in function update
[13] @scripts/boot.lua:852: in function game_update
[14] @scripts/boot.lua:615:in function
<>
```