[Dev 2513] Removing a non-build ladder

reproduce this error:

  1. build a ladder to a roof
  2. remove this ladder, before it is built

error code

develop-2513 (x64)radiant/modules/entities.luac:86: attempt to index local ‘entity’ (a nil value)stack traceback:
[C]: ?
radiant/modules/entities.luac:86: in function ‘get_world_grid_location’
…tonehearth/services/server/build/ladder_builder.luac:58: in function ‘_get_climb_to’
…tonehearth/services/server/build/ladder_builder.luac:71: in function ‘_update_ladder_tasks’
…tonehearth/services/server/build/ladder_builder.luac:52: in function ‘remove_user_removable_point’
…tonehearth/services/server/build/ladder_manager.luac:19: in function ‘remove_user_created_ladder_portion’
stonehearth/services/server/build/build_service.luac:280: in function <stonehearth/services/server/build/build_service.luac:278>

Confirmed geezzzzzzzzzzzzzz needs to be 20 characters!!!