[BUG?]Very simple vehicle can be used as ladder.

[yuganxia]

# Describe the bug
Very simple vehicle can be used as ladder.

# Steps To Reproduce

1. Create a vehicle with whatever frame
2. Attach a wing mirror/spike/wooden spike or whatever foldable and climbable vpart next to the frame.
3. Remove the frame
4. Put it next to a building step on it
5. now you can climb the building by press <.
6. This little ladder even can be folded and put into your bag.

# Expected behavior
That is kind of hilarious.
I can climb on a building by step on a thing which less than 0.5L after folded.
That make stepladder in game useless.

# Screenshots

# Versions and configuration

• OS: Windows
  • OS Version: 10.0 1809
• Game Version: 0.E-1970-g3278b58 [64-bit]
• Graphics Version: Tiles
• Game Language: English [en]
• Mods loaded: [
  Dark Days Ahead [dda],
  Disable NPC Needs [no_npc_food]
  ]

# Additional context
Game will crash in #10647 (which will not in 0.E stable) when you try to step on your fodable ladder.

src/generic_factory.h:404 [int_id<T> generic_factory<T>::convert(const string_id<T>&, const int_id<T>&) const [with T = ter_t]] invalid terrain id "wing_mirror"
09:50:26.335 ERROR : src/generic_factory.h:404 [int_id<T> generic_factory<T>::convert(const string_id<T>&, const int_id<T>&) const [with T = ter_t]] invalid terrain id "wing_mirror"
09:50:27.775 ERROR : src/generic_factory.h:404 [int_id<T> generic_factory<T>::convert(const string_id<T>&, const int_id<T>&) const [with T = ter_t]] invalid terrain id "wing_mirror"
09:50:28.297 ERROR : src/generic_factory.h:404 [int_id<T> generic_factory<T>::convert(const string_id<T>&, const int_id<T>&) const [with T = ter_t]] invalid terrain id "wing_mirror"
09:50:34.936 ERROR : src/generic_factory.h:404 [int_id<T> generic_factory<T>::convert(const string_id<T>&, const int_id<T>&) const [with T = ter_t]] invalid terrain id "wing_mirror"
09:50:35.472 ERROR : src/generic_factory.h:404 [int_id<T> generic_factory<T>::convert(const string_id<T>&, const int_id<T>&) const [with T = ter_t]] invalid terrain id "wing_mirror"
09:50:49.991 ERROR : src/generic_factory.h:404 [int_id<T> generic_factory<T>::convert(const string_id<T>&, const int_id<T>&) const [with T = ter_t]] invalid terrain id "wing_mirror"
09:50:51.592 ERROR : src/generic_factory.h:404 [int_id<T> generic_factory<T>::convert(const string_id<T>&, const int_id<T>&) const [with T = ter_t]] invalid terrain id "wing_mirror"
09:51:07.879 ERROR : src/generic_factory.h:404 [int_id<T> generic_factory<T>::convert(const string_id<T>&, const int_id<T>&) const [with T = ter_t]] invalid terrain id "wing_mirror"
09:51:08.615 ERROR : src/generic_factory.h:404 [int_id<T> generic_factory<T>::convert(const string_id<T>&, const int_id<T>&) const [with T = ter_t]] invalid terrain id "wing_mirror"
09:51:38.136 ERROR : (error message will follow backtrace)

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions. Please do not 'bump' or comment on this issue unless you are actively working on it. Stale issues, and stale issues that are closed are still considered.

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions. Please do not 'bump' or comment on this issue unless you are actively working on it. Stale issues, and stale issues that are closed are still considered.

[int-ua]

Still an issue in latest experimental.