decoder/nanocbor_leave_container(): reject (some) invalid arguments

[mguetschow]

The documentation of nanocbor_leave_container() states the following preconditions:

This must be called with the same @ref nanocbor_value_t struct that was used to enter the container (1). Furthermore, the @p container must be at the end of the container (2).

This PR adds a check to the implementation to (partly) ensure these preconditions and otherwise return an error code. To this end, the API is changed in a backwards-compatible manner with int as return type instead of void.

The check ensures that container is actually a container and that it has been consumed up to the end (precondition (2)). It also adds a plausibility check for (1) by ensuring that container->curr is between it->curr and it->end.

I'm not sure whether the selected error value NANOCBOR_ERR_INVALID_TYPE is the appropriate one, maybe it would make sense to add NANOCBOR_ERR_INVALID_ARGUMENT or something similar to nanocbor_error_t.