`ls-file-collection annexworktree`: iterable did not yield matching item for route-in item

[mih]

Reproduce by running:

❯ datalad ls-file-collection annexworktree .
[ERROR  ] iterable did not yield matching item for route-in item, cardinality mismatch? 

on any non-annex repo. Arguable this makes not much sense, but it is nice to not have to perform repo-type checking upfront. Also, the error message does not say "not supported", but something complicated/unrelated instead.

From @mih on Matrix:

[This is ] an issue in the iterator implementations. We did not foresee that a command fails entirely. in this case, we are running git annex find via iter_git_subproc, which fails with git-annex: First run: git-annex init. This in turn leads to a strange routing error, because the underlying error is not caught. [...]

I think the easiest from the perspective of the implementation of a fix would be to run something like git annex info --fast -q upfront, and if that fails, just yield the underlying generator.