0-length paths aren't explicitely forbidden but break most endpoints

[eckter]

What happened?

Nothing in the API or UI forbids the user from creating a path with overlapping origin and destination, resulting in a 0-length path.

Surprisingly, the pathfinding endpoint gives a valid result. But any subsequent call (path_properties or simulation) result in a 500.

I don't think it's a significant issue. But if we want to handle that case properly, we could add an error case in the pathfinding endpoint.

What did you expect to happen?

I expected it to fail right away at the pathfinding endpoint.

I think we should either fail with a 4xx at the pathfinding endpoint, or handle it all the way (but let's not do that).

How can we reproduce it (as minimally and precisely as possible)?

Rocket tool, pick any OP, then ask for a path like MES MES on small_infra

On which environments the bug occurs?

Local

On which browser the bug occurs?

Firefox

OSRD version (top right corner Account button > Informations)

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